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Time to Platinum: 35 Hours
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Difficulty: 5/10
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Trophies: 37 (1 Platinum, 5 Gold, 9 Silver, 22 Bronze)
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Missable Trophies: 0
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Online Trophies: None
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Number of Playthroughs: 1
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Format: PS4
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Glitches Encountered: 0
Trophy
Guide

Trophy Guide Overview
First of of, let me say that this game is fantastic, and to push into legendary status, it is an extremely enjoyable and straightforward platinum. As of writing this (April 2018,) this is my favourite game of the year, but Red Dead Redemption 2 could change all that in October, we'll have to see.
There are no missable trophies, and the whole game can be played on easy difficulty, so you can approach this list in any way that you would like. I have created a collectible walkthrough guide HERE that minimises the amount of back-tracking you'd need to do that I recommend you use. I'll list below the order that I did things, I found this to be the most efficient way to get through the game, but also, this is the sort of game you won't want to rush through, you'll want to soak it all up, so don't feel you have to do the same way I did.
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Finish the main story (Journey,) while picking up any collectibles along the way.
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Finish all of the side missions (Favors) for Brok and Sindri, while finding any collectibles along the way.
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Explore the Lake of Nine, finding all of the collectibles
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Free the three dragons (Dangerous Skies trophy)
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Do all of the favors for the spirits around the Lake of Nine (Unfinished Business trophy)
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Travel to Muspelheim and do all of the trials (Fire and Brimstone trophy)
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Travel to Niflheim and open all of the chests inside the centre of the workshop (Darkness and Fog trophy)
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Deafeat all of the Valkyries (Chooser of the Slain trophy)
The Order Which I Unlocked the Trophies
01 - The Journey Begins
02 - Nice Moves
03 - Dwarven Ingenuity
04 - A New Friend
05 - Enchanted
06 - Best Dressed
07 - Feels Like Home
08 - Dragon Slayer
09 - Troubling Consequences
10 - Hello, Old Friend
11 - Promise Fulfilled
12 - Round 2
13 - Past Haunts
14 - Trilingual
15 - Twilight Beckons
16 - Last Wish
17 - Path of the Zealot
18 - Primordial
19 - Quick Tempered
20 - Like Oil and Water
21 - Iðunn's Orchard
22 - All Will Fall
23 - Beneath the Surface
24 - Curator
25 - Death Happened Here
26 - Dangerous Skies
27 - Treasure Hunter
28 - The Truth
29 - Allfather Blinded
30 - Unfinished Business
31 - The Best Moves
32 - Fire and Brimstone
33 - Why Fight It?
34 - Darkness and Fog
35 - Worthy
36 - Chooser of the Slain
37 - Father and Son

Father and Son
Obtain all other trophies

As with all platinum trophies this will unlock once you have collected the rest.

The Journey Begins
Defend your home from The Stranger

Secret Trophy
Story related and can't be missed.
This trophy will unlock after you have finished the first story (journey) mission of the game 'The Marked Trees'.

A New Friend
Survive the Witch's Woods

Secret Trophy
Story related and can't be missed.
You'll unlock this trophy mid-way through the story (journey) mission 'Path to the Mountain'.

Feels Like Home
Allow the Light Elves to return home

Secret Trophy
Story related and can't be missed.
This trophy will unlock near the end of the story (journey) mission 'The Light of Alfheim'.

Dragon Slayer
Defeat the Dragon of the Mountain

Secret Trophy
Story related and can't be missed.
This trophy will unlock once you have beaten the main boss during the story (journey) mission 'Inside the Mountain'.

Troubling Consequences
Defeat Magni and Modi

Secret Trophy
Story related and can't be missed.
You'll unlock this trophy after the main boss fight at the end of the story (journey) mission 'The Magic Chisel'.

Hello, Old Friend
Retrieve the Blades of Chaos

Secret Trophy
Story related and can't be missed.
You'll unlock this trophy near the beginning of the story (journey) mission 'The Sickness'.

Promise Fulfilled
Heal Atreus

Secret Trophy
Story related and can't be missed.
This trophy will unlocked upon completing the story (journey) mission 'The Sickness'.

Round 2
Rescue Atreus

Secret Trophy
Story related and can't be missed.
This trophy will unlocked upon completing the story (journey) mission 'Return to the Summit'.

Past Haunts
Ride the ship out of Helheim

Secret Trophy
Story related and can't be missed.
This trophy will unlocks right near the end of the story (journey) mission 'Escape From Helheim'.

Twilight Beckons
Defeat Baldur

Secret Trophy
Story related and can't be missed.
This trophy will unlocked upon completing the story (journey) mission 'Jötunheim in Reach'.

Last Wish
Spread the ashes

Secret Trophy
Story related and can't be missed.
This trophy will unlocked upon completing the story (journey) mission 'Mother's Ashes'.

Beneath the Surface
Explore all the Lake of Nine has to offer

If you are planning on finding all of the collectibles needed for trophies, then this trophy can't be missed.
Lake of Nine is the 'central hub world' of the game with Tyr's Temple in the centre. It is probably a good idea to explore this area once you have finished the main story, or at least wait until the second water drop, as the enemies on the islands and beaches are quite a high level.
The places you need to visit and discover are:
Buri's Storeroom (East)
Cliffs of the Raven (South East)
Forgotten Caverns (North West)
Iron Cove (South West)
Isle of Death (South West)
Light Elf Outpost (North West)
Lookout Tower (South)
Ruins of the Ancient (Far North West)
Stone Falls (East)

Death Happened Here
Fully Explore Veithurgard

To get to Veithurgard itself, you'll need to open the large gates found near Stone Falls, you can only do this after the second water drop. Once they're open you'll go through the gates and navigate Veithurgard Pass. Once you're out the other side of the pass and back in your boat, you're in Veithurgard. You will need to come to Veithurgard to free one of the dragons for the 'Dangerous Skies' trophy.
To get this trophy you need to open the castle doors, work your way through the castle, defeat the troll Daudi Hamarr and open the chest that is through the double doors at the back of the area where you fought Daudi Hamarr. Once you open the chest, the trophy should unlock.


Trilingual
Learn the languages of Muspelheim and Niflheim

To learn the two languages, you need to open 8 language cipher chests (4 for each), the first 4 you open will have Muspelheim language ciphers in them, with Niflheim language ciphers being in the next 4. There are way more than eight of these chests (gold in colour, with a purple haze around them) in the game, with ones you open after collecting all the ciphers giving you handy materials and items. These chests are needed to actually access Muspelheim and Niflheim later in the game.
I have created a collectibles walkthrough guide for this game HERE. Following this guide will net you the first eight cipher chests you'll come across.

Dwarven Ingenuity
Upgrade a piece of armor

You'll more than likely unlock this trophy naturally, as upgrading armour is something you'll want to be doing before taking on any of the later bosses or Valkyries.
To upgrade a piece of armour simply go to see either Brok or Sindri at their shop. When in the shop menu go to the upgrade tab and choose a piece of armour to upgrade, and as long as you have enough hacksilver, you just need to hold square and upgrade it once for the trophy to unlock.

Nice Moves
Obtain a Runic Attack Gem

This is another trophy that you are pretty much guaranteed to unlock. Runic Attack Gems can be found all over the place in Legendary chests (large ornate gold chests.) The first one you'll come across is during 'Path to the Mountain' in 'Wildwood's Edge,' it's just to the right of main path, basically unmissable.
Once you open the chest you'll be given a short tutorial on how to equip it to your weapon, once you've done that, the trophy will unlock.

Iðunn’s Orchard
Fully upgrade your health

To upgrade your health to the maximum, you'll need to find 9 Iðunn apples. They can be found in Nornir chests thoughout the game. For more information on these, see the trophy 'Quick Tempered' below.

Quick Tempered
You knocked out 3 or more enemies with a single fart outside of battle.

As with 'Iðunn’s Orchard' above, you'll need to open Nornir chests, this time you'll need to find 9 Horns of Blood Mead. So that's 18 Nornir chests in total, like the cipher chests, there are way more than you need in the game.
Nornir chests are easily recognised, as they have three blue runic marks on the front of them. You'll need to complete a very simple puzzle before you can open each Nornir chest. The puzzles will either be finding three runes that match the ones on the chest and breaking them, they usually aren't far from the chest, or hitting three bells with rune marks on them in quick succession, again, they will be close to the chest.
I have created a collectibles walkthrough guide for this game HERE. Following this guide will net you the first 18 Nornir chests you'll come across.

Best Dressed
Craft an outfit for Atreus

To craft an outfit for Atreus, you'll need to go to either Brok or Sindri's shop. Once there, go to the crafting section of the menu and choose Atreus in the top left. As long as you have enough hacksilver and materials, you can hold square to craft him a new outfit, once you've done that, the trophy will unlock.

Enchanted
Slot an Enchantment into your armor

You will find enchantments everywhere, they are in chests, dropped by tougher enemies and you can even purchase them from Brok and Sindri. As soon as you find them you'll want to equip them, as they can give you some really handy passive abilities.
All armour has at least one enchantment slot, with some pieces of armour having three slots. To equip an enchantment, simply go to the 'armor' menu, choose a piece of armour and press square, now as long as you have an enchantment you can equip it and you'll get the trophy.

All Will Fall
Kill 1,000 Enemies

I'd say that if you are going for the platinum in this game, then you're guaranteed to unlock this trophy without trying. If you wish to keep an eye on this trophy you can do in the 'Goals' section of the menu. Look for the 'Wages of War' labor and it'll tell you how many enemies you've killed there.

Dangerous Skies
Free all of the Dragons

There are three dragons that you need to freed around Midgard for this trophy:
Reginn - Konunsgard Stronghold - The Fire of Reginn
Otr - Veithurgard - The Imprisonment of Otr
Fafnir - North Lake of Nine - The Flight of Fafnir
You can't access the dragons until later in the story, Otr is available after the first water drop of Lake of Nine, but you'll have to wait until the second drop before you can access Reginn and Fafnir. Reginn is only accessible once you have started the 5th favor for Brok and Sindri, as you'll need an entry stone to Konunsgard from them.
Actually freeing the dragons is very straight forward. They are restrained by a magic anchor, with each anchor being powered by three shrines that you'll have to destroy. If you would like a more detailed look at the locations of the dragons and how to free them, please see my video below:

Like Oil and Water
Complete all of Brok and Sindri's Favors

You'll meet Brok and Sindri during the main story line. They are both blacksmiths, who can craft you armour and weapons, as well as upgrading the items you already have. After a certain point in the story they will offer a side quest (favor), they have two side quests each, along with a final one that you'll need to wait until they are reunited before you can start. You have to finish two for Brok and Two for Sindri before they offer you the final one. The quests are as follows:
Second Hand Soul
Giver: Brok
Location: Volunder Mines
First Available: After the first water drop of Lake of Nine
Main Objective: Find Brok's friend... or what's left of him
Deus Ex Malachite
Giver: Brok
Location: Landsuther Mines
First Available: After completing 'Second Hand Soul' and the second water drop of Lake of Nine
Main Objective: Help Brok find what he's looking for
Fafnir's Hoard
Giver: Sindri
Location: Fafnir's Storeroom
First Available: After completing the Alfheim part of the main story
Main Objective: Help Sindri find Fafnir's whetstone
Family Business
Giver: Sindri
Location: Northri Stronghold
First Available: After completing 'Fafnir's Hoard' and 'The Sickness' part of the main story
Main Objective: Retrieve the whetsone
Hail to the King
Giver: Brok and Sindri
Location: Konunsgard Stronghold
First Available: After completing 'Deus Ex Malachite' and 'Family Business', and after Brok and Sindri have reunited
Main Objective: Retrieve the ingredients to craft the Dwarven armour of legend

Curator
Collect all of the Artifacts

There are only 45 artefacts in the game, as far as collectibles go, that's not bad. They are spread out over different locations though. None of them are missable, as you can go back to most locations at any time and you can travel everywhere once you've finished the main story.
I would advise that you use my collectible walkthrough (HERE) to minimise on back-tracking later on. You can keep an eye on all collectibles for each area in the pause menu.

Allfather Blinded
Kill all of Odin's Ravens

There are 51 ravens scattered around all over Midgard. Again, none of them are missable, and you can collect any that you may have missed after you've finished the main story. Unlike the artefacts, the ravens can be a bit trickier to spot, as they are really light greenish blue and are easily missed when in looking against the sky for them. You'll more than likely hear them before you see them.
I would advise that you use my collectible walkthrough (HERE) to minimise on back-tracking later on. You can keep an eye on all collectibles for each area in the pause menu.

The Best Moves
Fully upgrade a Runic Attack

Runic attacks are fundamental part of the combat in God of War. They are very powerful attacks that can help make short work of most enemies, so you should be upgrading them as soon as possible. Having said that, I completely forgot that you could upgrade them, and didn't do until I had nearly finished the game.
To fully upgrade a Runic attack, you'll need to upgrade it twice, to level 3. This can be done at any time by spending XP, in weapons part of the pause menu. The last upgrade can be quite expensive, so make sure you invest in something you are going to use, like Frost Giant's Frenzy, by far my favourite.

Worthy
Fully upgrade the Leviathan Axe

You upgrade your Leviathan Axe by using materials found during the main story called 'Frozen Flames'. Once you find one, you can upgrade your axe at either Brok or Sindri's shop. You only need one per upgrade, they are dropped by certain bosses throughout the story, so they are quite rare. Upgrading your axe to level 5 is unmissable, because if you forget to pick up any of the Frozen Flames, you can find them in the 'Lost Items' part of Brok or Sindri's shop. To get your axe to the 6th and final level however, takes a bit more work.
You'll need to head to Niflheim, open up the central central chamber and look for something called 'Chilling Mist of Niflheim,' which can be exchanged for the last Frozen Flame at Sindri's shop in the resources section. For more information on everything Niflheim, please see the 'Darkness and Fog' trophy below.

Why Fight It?
Fully upgrade the Blades of Chaos

Upgrading the Blades of Chaos is pretty much the same as the Leviathan Axe, apart from this time you'll need materials called 'Chaos Flames.' These are found during the story also, and as with the Frozen Flames, if you forget to pick one up, you can find it in the 'Lost Items' section of Brok or Sindri's shop. Once you've finished the story the Blades will be at level 4, one lower than the axe. Again, getting the 5th and final upgrade will take a bit more work.
This time you'll need to head to Muspelheim. You will need to complete the first five normal and hard challenges, followed by the 6th challenge, defeat the Valkyrie Gondul, who will drop an item called the 'Raging Inferno of Muspelheim.' you will need to trade this with one of the dwarfs for the last Chaos Flame in the resources section of their shop. For more information on everything Muspelheim, please see the 'Fire and Brimstone' trophy below.

Path of the Zealot
Obtain Traveler armor set

The traveller armour set is a legendary armour set comprised of three parts: Breastplate of the Traveller, Gauntlets of the Traveller and War Belt of the Traveller. In order to be able to craft the armour, you'll need to defeat travellers, pictured below:

They can be found all over Midgard, but if you are struggling to find them, you can usually find them on top of the towers around the Lake of Nine. They are quite tough enemies and won't go down without a fight, but once they do, they'll drop Traveller's Armor Shards and Traveller's Grisly Trophies, both of these materials, plus a lot of hacksilver are what you'll need to take to Brok or Sindri to craft the armour. Before you can craft the armour set you'll need to speak to Brok or Sindri using the triangle button to complete the labor 'The Road Less Travelled'. Once that's done you're ready to craft. The materials you'll need are as follows:
Breastplate of the Traveller - 16400 hackilver and 5 Traveller's Armour Shards
Gauntlets of the Traveller - 12800 hacksilver, 18 Traveller's Grisly Trophies and 3 Traveller's Armour Shards
War Belt of the Traveller - 12800 hacksilver and 12 Traveller's Grisly Trophies

Primordial
Obtain Ancient armor set

The ancient armour set is a legendary armour set comprised of three parts: Pauldron of the Ancient, Gauntlets of the Traveller and War Belt of the Traveller. In order to be able to craft the armour, you'll need to defeat ancients, pictured below:

Just like Travellers, they can be found all over Midgard. You even fight one quite early on in the story. They can not be defeat by normal combat means, you'll need to wait until they expose their chest and then throw your Leviathan axe at the glowing part in the centre. Once you have defeated one, it'll drop an Ancient Heart and Ancient rubble, both of these materials, plus a lot of hacksilver are what you'll need to take to Brok or Sindri to craft the armour. Before you can craft the armour set you'll need to speak to Brok or Sindri using the triangle button to complete the labor 'Hearts of Stone.' Once that's done you're ready to craft. The materials you'll need are as follows:
Pauldron of the Ancients - 12800 hacksilver and 3 Ancient's Hearts
Gauntlets of the Ancients - 9600 hacksilver and 8 Ancient's Rubble
Belt of the Ancients - 9600 hacksilver and 8 Ancient's Rubble

Unfinished Business
Assist all of the wayward Spirits

There are five favors that you'll need to complete favors for various spirits around the Lake of Nine for this trophy. They are:
Time Heals All
Giver: Scroll at Northri Stronghold
Location: Fafnir's Storeroom
First Available: Pick up the scroll during the 'Family Business' Favor
Main Objective: Return to the spirit in Fafnir's Storeroom
Unfinished Business
Giver: Brazier
Location: Lake of Nine
First Available: After the first water drop of Lake of Nine
Main Objective: Explore the islands of the lake (four)
The Anatomy of Hope
Giver: Wayward Spirit
Location: Mason's Channel
First Available: After second water drop of Lake of Nine
Main Objective: Recover Gullveig's bones and return them to the spirit
Dead Freight
Giver: Tradesman Spirit
Location: Forgotten Caverns
First Available: After second water drop of Lake of Nine
Main Objective: Kill three Hel-Walker Crews
Hammer Fall
Giver: Disciple of Thor
Location: Stone Falls
First Available: After first water drop of Lake of Nine
Main Objective: Destroy the statue of Thor
For a walkthrough of each favor, please see my video guide below:

Treasure Hunter
Use treasure maps to find all of the dig spots

There are 12 treasure maps spread out all over the game, which means there are also 12 dig spots you'll need to find as well. If you know where a certain dig spot is, but you don't have the map yet, you can't dig up the treasure, you need to obtain the maps first. The maps and their corresponding dig spot are as follows:
Kneel Before Thor!
Treasure available: After second water drop
Map Location: Landsuther Mines
Treasure Location: Lookout Tower
Don't Blink
Treasure available: After returning to the 'Black Breath' with the Alfheim light
Map Location: Fafnir's Storeroom
Treasure Location: Foothills
Finder's Fee
Treasure available: During 'Family Business' Favor
Map Location: Forgotten Caverns
Treasure Location: Northri Stronghold
Njord's Oarsmen
Treasure available: After second water drop
Map Location: Northri Stronghold
Treasure Location: Njord's Oarsmen
The Turtle's Tribute
Treasure available: During return visit with Mimir's head
Map Location: Witch's Cave
Treasure Location: River Pass
Hunter's Kingdom
Treasure available: After first water drop
Map Location: Lookout Tower
Treasure Location: Veithurgard
Creation Island
Treasure available: After second water drop
Map Location: Iron Cove
Treasure Location: Buri's Storeroom
Dead and Bloated
Treasure available: After first water drop
Map Location: Volunder Mines
Treasure Location: Cliffs of the Raven
Island of Light
Treasure available: After second water drop
Map Location: Helheim Tower Beach
Treasure Location: Light Elf Outpost
The Boat Captain's Key
Treasure available: After first water drop
Map Location: Stone Falls
Treasure Location: Isle of Death
The Last Place They'd Look
Treasure available: After second water drop
Map Location: The Mountain
Treasure Location: Council of Valkyries
The Historian
Treasure available: After second water drop
Map Location: Ruins of The Ancient
Treasure Location: Fafnir's Storeroom
I would advise that you use my collectible walkthrough (HERE) to minimise on back-tracking later on.

The Truth
Read all of the Jötnar shrines

There are 11 Jötnar shrines to find though-out the game. They are easily recognised, they look like large wooden cabinets. All you need to do is press square near one and Atreus will read it, adding the lore to his journal.
I would advise that you use my collectible walkthrough (HERE) to minimise on back-tracking later on.

Fire and Brimstone
Complete all of the Trials of Muspelheim

The description of this trophy is a little misleading, as you don't need to complete 'all' of the trials, you only need to do 3 out of the 5 impossible trials, plus the final challenge on top of the volcano. You do however need to do all of the normal and hard challenges, plus defeat the Valkyrie.
To gain access to Muspelheim, you'll need to collect the four Muspelheim language ciphers, see the 'Trilingual' trophy for more information on that. Once you have them, you'll have to use the bi-frost in the realm travel room to actually travel to Muspelheim.
Once there, you'll eventually come across Brok and his shop. I'd make sure that everything you have is fully upgraded and that you have a Resurrection stone, just in case you die mid-trial. Once you're ready head up the hill and through the gate to start the trials. The realm is basically a linear path broken up by 6 combat areas. You'll need to complete the normal and hard trial in each arena before moving on. So you'll be doing 10 trials as you move up the volcano, then when you're at the top you'll fight a Valkyrie (needed for the 'Chooser of the Slain' trophy.) After you've done that you'll unlock the impossible trials, one for each of the 5 arenas. Teleport back to the bottom of the volcano again, and start working your way back up again completing impossible trials as you go. There are 5 impossible trials, but as I mentioned earlier, you only need to complete 3 to unlock the final challenge at the top of the volcano where you fought the Valkyrie. So once you've completed 3, you can just skip the rest and run (or teleport) to the top of the volcano. Finish the last trial up there and you'll unlock the trophy. I've listed the trials below in order you'll come across them.
Trial I (Normal): Time Attack
Objective: Defeat 15 enemies within 3:00
Trial I (Hard): Resurrection
Objective: Defeat enemies in quick succession
Trial II (Normal): Survival
Objective: Survive for 5 Minutes
Trial II (Hard): Stunner
Objective: Defeat enemies while they quickly regenerate health
Trial III (Normal): Shield Breaker
Objective: Kill grunts to break the Elite's shield (five waves)
Trial III (Hard): Location Challenge
Objective: Kill enemies while they are inside the gold rings (three waves)
Trial IV (Normal): 100 Enemy Challenge
Objective: Defeat 100 enemies
Trial IV (Hard): Protector
Objective: Don't let enemies capture Atreus (three waves)
Trial V (Normal): Time Slips Away...
Objective: Kill enemies to increase time (two waves)
Trial V (Hard): Untouchable
Objective: Defeat all enemies without taking damage
Trial VI: Valkyrie Gondul
Objective: Defeat the Valkyrie
Trial I (Impossible): Untouchable
Objective: Defeat 20 enemies without taking any damage
Trial II (Impossible): Time Attack
Objective: Kill enemies before time runs out
Trial III (Impossible): Kill Location Challenge
Objective: Kill enemies while they are inside the gold rings
Trial IV (Impossible): Stunner
Objective: Kill all enemies while they quickly regenerate health
Trial V (Impossible): Time Slips Away...
Objective: Kill enemies to increase time
Trial VI (Impossible): Gauntlet
Objective: Defeat 50 enemies as quickly as possible (There are other objectives, but you just need to complete the first one for the trophy)

Darkness and Fog
Retrieve all treasure from the Workshop's center chamber

Before you can even attempt this trophy, you'll need to gain access to Niflheim by collecting four Niflheim language ciphers. They will be the second lot of four that you collect, with Muspelheim ciphers being the first. see the 'Trilingual' trophy for more information on that. Once you have them, you'll have to use the bi-frost in the realm travel room to actually travel to Niflheim.
Niflheim is essentially one big randomised gauntlet that you need to fight your way through while the low-lying fog slowly poisons you. Sounds fun... right? It actually sounds a lot worse than it is. The whole time that you are in the gauntlet there will be a pink bar at the top of the screen that slowly goes down, and I mean slowly, I haven't actually timed it, but I reckon it's a good two - two and half minutes. Once this bar does deplete however, you will start to die. The good news is that you fill it up a little bit every time you open a chest. If you do die while in the gauntlet area, you will lose any mist echoes (the 'currency' of Niflheim) that you haven't yet banked by leaving the area.
As I mentioned before the whole area is randomised. Think of it as a large square with the workshop in the centre and the gauntlet surrounding it. In-between the enemy areas there are circular blade and wall traps linking them, these change every time you re-enter. As well as there being the four corners of the square area to battle enemies, there are also two off-shooting areas with higher level enemies, but also higher rewards. One of the off-shoot areas will contain a Valkyrie until you defeat her, which you will need to do for the 'Chooser of the Slain' trophy. So basically what you'll want to do, starting at Sindri's shop, is do a full circuit of the gauntlet, opening all the chests that you can find (you'll need to defeat any enemies in the area before you can open them), then return to Sindri, leaving the foggy area and this will bank any mist echoes that you have collected.
Now, what to do with all those mist echoes you've been collecting. Firstly, you'll need to spend 500 mist echoes at Sindri's shop to acquire the entry stone to the central area. Once you've done that, you'll need to use the stone and enter the central chamber. Here you'll find 5 chests and 3 realm tears. They all cost a specific amount of mist echoes to open (70,000), and you need to open them all for the trophy. This may sound like a lot of grinding, but it's not that bad. You may have noticed that you've been picking up some resources as well out of the chests. If you go to Sindri's shop, you'll see that you can sell these resources for a lot of mist echoes, and I'd advise that you do so. To open the realm tears, you also need something called an anchor of fog, you'll need three of these, one for each tear. You randomly get these from opening chests, so you'll have to keep going around the workshop until you have enough of these. I reckon you'll need to do about four laps of the workshop to acquire enough mist echoes and anchors. Once everything has been opened in the central chamber, the trophy will unlock.

Chooser of the Slain
Defeat the nine Valkyries

Before you can fight any of the Valkyries you'll need to have finished the story mission 'The Magic Chisel' and obtain the chisel itself. This is because the Valkyries are locked away in Hidden Chambers of Odin and you need the chisel to open them.
There are eight 'regular' Valkyries and one queen Valkyrie. Four of them are located in Midgard, then there on in each of the following realms, Alfheim, Helheim, Muspelheim & Niflheim. For more information on the location of each Valkyrie, please see my videos below. To fight the the queen you'll need to defeat the other eight Valkyries and take their helmets to the council of Valkyries, which is located in the north of Lake of Nine, again see my video below for more information on that.
They are all tough opponents and you'll need to be a high level with good armour and enchantments to even stand a chance. Saying that though, they are all more than beatable. Each Valkyrie has a different fighting style, with the queen Valkyrie using every fighting style of the previous eight. My best advice to you is to study there moves and how to respond accordingly, knowing when to dodge, block, or use Atreus' arrows.
My 'loadout' for the fight against the queen was: (This fight was the last thing I did in the game)
Chest Armour: Pauldron of the True Warrior (Eye of the Outer Realm, Tyr's Shard & Asgard's Shard of Existence enchantments)
Wrist Armour: Gauntlets of the Valkyrie (Eye of the Winged Chosen & Ivaldi's Corrupted Mind enchantments)
Waist Armour: Waist Guard of the Valkyrie (Andvari's Soul & Heart of the Valkyrie enchantments)
I used the Runic attacks Njörd's Tempest as my light runic attack and Frost Giant's Frenzy as my heavy attack for every Valkyrie.