Monster Train

Working with KrakenScorch here is a combined guide:

Your best bet to collect this achievement is through mutators. The following will help a lot:
1. "Two for One" (every time you draft a card you gain 2 copies of it.)
2. "Come Prepared" (adds 12 random cards to your starting deck.)
3. "Burn Bright" (+2 Energy per turn). This extra energy will help you deal with higher cost random cards that would likely otherwise be a dead card in early game.

Since this run includes random cards, it may be helpful to have cards that have "Consume". If a card does not have have it, it can be added at the Merchant of Magic with a Surgestone (20 gold).
Another helpful aspect to be on the lookout for are Draw cards, as this will help you navigate your deck during the run.

Another thing to keep in mind during the run is to consider taking the +Draw artifact from the mini-boss stages. Another viable option would be the +Space artifact if your run has a lot of unit cards.

Overall the goal should be to grab cards that compliment your deck and duplicate cards where you can and it makes sense.

KrakenScorch's original guide strongly recommended using a run with the Hellhorn as primary and the Awoken as secondary.

One proposed challenge run is the following:
CottagesBasementExternal

The basic premise of the build is Hornbreaker with the following:
Armor 10 and Multistrike 1
Slay: Gain 10 Armor
Revenge: Gain Rage 3
Put it in either in the front or behind an imp or two and build its rage while adding armor to it.
I picked up Animus of Will and Shattered Shell for some added power behind Hornbreaker / on the other floors.

Run Details:

Artifacts (in order of collecting)
Imp-cicle
Blood for Blood
Light of Seraph
Ashes of the Fallen (Rage Imps with this kicks Hornbreaker into high gear)
Concussive Coals
Scorching Restraints (MORE RAGE)
Heaven's Gold
Light of Seraph
Tempered Talisman

Cards:
Hornbreaker
Animus of Will - Heartstone and Strengthstone
Animus of Will - Heartstone
Impish Scholar
Molting Imp
Shattered Shell - Frenzystone and Strengthstone
Shattered Shell
Train Steward x4
Welder Helper
Dark Deal - Stackstone and Ember (would have had two but screwed up the second one by adding a Surgestone, do NOT do this as it adds 20 to the damage part of the card...which would damage your unit)
Fortify x2
Invigorating Solution
Steel Enhancer x2
Vent x2
Vine Grasp - Surgestone
Vine Grasp
Engraft
Glimmer
Hidden Passage
Imp-Pressive - Surgestone and Eternalstone
Imp-Pressive - Surgestone
Pyre Shards x4
Restore x5
Torch x5
Adaptive Mutation
Sharpen - Emberstone
Sharpen
Reinforce - Emberstone

A Shardtail Queen + Rootseed Awoken with Come Prepared, Hivemine, and Two for One mutators custom challenge run is also a really easy way to get this achievement.

The general strategy is to give her at least one Imperialist at the Dark Forge so you can burn all the minion cards in your deck, and Imp Parade for the rest of the Dark Forges so you can spam build up rage on her. You’ll want to increase floor size, rage, and imp synergy stuff (Imp-olate works great!) while purging cards that don’t help with this (making sure you still have 40+ by the end so focus on purging spells instead of unit cards since they can still be burnt by the Shardtail Queen).



The seed that was super easy for me is EnzymeSensorDrops, which worked great because it gives you imp-olate and in this run you’ll be no costing and holdovering the spell to do a massive amount of damage.

I did the following (didn’t optimise it, but I got through real easy):

Dark Forge Imperialist on Shardtail Queen
Herzal’s Hoard Thorn Casing

Turn ON trials for every fight.

I put the Shardtail Queen at the top floor, usually at the back of the units. When a Cupid appears, if you’re lucky use a damaging spell card or the molting imp on it. Should be able to do this without getting any damage on the Pyre

Clan Pack the Fledgling Imp and Wildwood Custodian

From now on place the two Wildwood Custodians on the top floor, protecting them with random minions, while the Shardtail Queen will be on the middle floor.

Left path, collect the money, Merchant Magic.
Keepstone and Emberstone in Imp-olate.
Powerstone one Imp-pressive
Re-roll
Powerstone the other Imp-pressive
Emberstone Rootseeds

Battle with Trial ON
Wildwood Custodian at top, protect them with Stewards, Shardtail Queen middle, rage her when you can, imp-olate/imp-restive higher health enemies, sting to clean up enemies that slip to the top floor, Vinegrasp or Molting Imp Conduit Redirector, and just spam the minions and rootseeds. Always use Imp-olate when you get it because of holdover even if there are no enemies on a floor.

Clan Pack Ritual of Battle, Skip Awoken Clan, Skip Unit Draft. (I skip because we get more cards that synergies better down the line)

Right Path
Hell bent Imp-olate
Skip Awoken Banner
Concealed Caverns purge Hidden Passage, gain Hellhorned, collect Spike of the Hellhorned ( apply this on Shardtail in battle when you can).

Battle Talos
Basically same area strategy as the last fight. Always Imp-olate. Like seriously a few Imp-olates on the boss kills it. A bit of damage is fine since we’ll collect a Pyre Remains.

Rare Pack Wildwood Tome, Skip Awoken, Herzal’s Compound

Left Path
Collect money, Herzal’s Hoard Channelheart, Pyre Remains
Dark Forge Imp Parade

Battle Trial ON
Same strat, Wildwood Tome Shardtail Queen and Steward protecting top floor. Burn the spare Stewards with Shardtail Queen. Be sure to get rid of Weight of Contrition when in hand. When the boss appears you should have two Imp-olates that will 1 turn KO it.

Clan Pack Pyre Chomper, Allie Clan Pack Preserved Thorns

Right Path
Collect Money, Merchant of Magic
Surgestone Glimmer
Emberstone Ritual of Battle
Re-roll
Emberstone the same Ritual of Battle
Powerstone second slot on an Imp-pressive
Freeze stone Spike if the Hellhorned
Purge Hidden Passage for 50
Concealed Caverns Umbra Stone
Go back to the Merchant of Magic and purge one Umbra Stone

Battle trial ON
Same strategy but now it’s viable to Ritual of Battle the Shardtail Queen with the Emberstone’d one. Also Umbrastone Shardtail if you’d like. Tbh the main damage is Imp-plosion at this point. When you get Spike of the Hellhorned you can hold onto it until you use Pyre Chompers so you can apply even more rage and armour.

Collect Scorched Steel
Clan Pack Imp-in-a-Box, Skip Allied Clan Pack

Right Path
Herzal’s Hoard Gnarled Root
Hellvent Imp-olate

Battle Fel
Usual strat. Before placing anything use Imp-in-a-Box. If you get Welder Helper use it on Shardtail Queen to stack some armour on her. Imp-olate boss. Always play Fledgling Imp on Shardtail floor to stack rage. Getting hurt by the penance shouldn’t matter too much since we’ll get back 20 health from an upcoming Pyre Remains.

Rate Pack Allot of the Ancients
Light of Seraph

Right Path
Unstable Vortex both Restoration Detonation
Hellvent Imp-olate
Pyre Remains
Dark Forge Imp Parade II

Battle Trial ON
Same strat. All the Imp-plate make a lot of strategising redundant hahaha.

Clan Pack Rage Serum, Allied Clan Pack Preserved Thorns

Right Path
Forgotten Boons, Hellvent Imp-olate

Merchant of Steel
Thornstone and Largestone the same single Train Steward (this one protects the Wildwood Custodians, the rest are fed to the Shardtail Queen)

Merchant of Trinkets
Buy Traitor’s Quill
Re-roll
Buy Unbroken Horn, Consumed Crown, and Scorching Restraints
Spend rest of money to purge Branding Rite and one of the NOT upgraded Root Seeds. If you somehow have enough money for another purge, purge the other not upgrade Root Seed.

Fight Seraph. The imp-olates that will make short work with him and the enemies. Basically the same strategy. Keep an eye out if he summons on the top floor and keep your Wildwood Custodians alive.

Once he dies and you light the frozen heart you should get the achievement as you’ve got 48 cards in your deck! :)