Monster Train

*This solution might no longer work as a patch has reset the seed and the levels are no longer loading up the same way as they did before*

This is rather simple with a custom match but to streamline it even more I have created a custom challenge which you can use to replicate this. You can also find Talos during this run for the Ta-ta Talos achievement as well as Archus for the Archpocalypse achievement.

You'll want to always put down your Champion and Guard of the Unnamed (once you get this card) first. Then play your spells to trigger the incant activity.

Challenge name: MacroTramadolJumping

---Limbo---
Take Handheld Totem upgrade for Champion
Take Sap Tap artifact

After battle #1:
Take Crypt Builder card

---Level 2---
Take the right path.
Upgrade Crypt Builder with Freezestone and Powerstone.
Take Guard of the Unnamed from the Stygian Banner.

After battle #2:
Take Ice Tornado card

---Level 3---
Tale the right path.
Upgrade Ice Tornado with a Powerstone (+10 Magic Power).
Re-roll and apply another Powersone to Ice Tornado making it 40 damage.
Purge a Train Steward.
From Caverns take "The small shard" and apply it to Guard of the Unnamed.

Battle with Talos
Turn 1
Bottom Floor Lineup: Champion -> Guard of the Unnamed -> Train Steward.
Use Energy Siphon on Talos.
Use Sting on bottom floor.
End Turn

Turn 2
Use Energy Siphon on Talos.
Use Frozen Lance 2x on bottom floor.
End Turn

Turn 3
Use Crypt Builder on Talos

You should get the Ta-ta Talos achievement here.

After battle #3:
Don't take any cards.
Take Fel's Remorse for +1 ember per turn.

---Level 4---
Take the right path.
Take Light's Gift artifact.
Purge 2 Train Stewards.
Take Handheld Totem II upgrade for champion.

After Battle #4:
Take Urchin Spines card

---Level 5---
Take the right path.
Add Permafrost to Urchin Spines.
Re-roll and add Eternalstone to Urchin Spines as well.
Take Precious Plating artifact.

After Battle #5:
Don't take any cards.

---Level 6---
Take the left path.
Don't take anything from Caverns.
Apply Doublestack and Embverstone upgrade to one Energy Siphon.
Apply Surgestone upgrade to a Sting card.
Purge 2 Restore cards.

Battle with Archus

Turn 1
Middle floor lineup: Champion -> Guard of the Unnamed
Use Urchin Spines on bottom floor with Archus.
Use Energy Siphon on Archus.

Turn 2
Use Ice Tornado on bottom floor.
Use Frozen Lance and Spikes on middle floor.

Turn 3
Use two Energy Siphon cards on Archus.
Use Crypt Builder on Archus.

This should end the battle and pop the Archpocalypse achievement.

After Battle #6:
Don't take any cards.
Take Hezral's Compound enhancement for +1 draw each turn.

---Level 7---
Take the right path.
Take the gold.
Take Founding Seal artifact.
Purge Glacial Seal and one Frozen Lance card.
Upgrade champion with Handheld Totem III for 6 spell weakness.

After battle #7:
Don't take any cards

---Level 8---
Take the right path.
Duplicate Urchin Spines.
Purge Restore and the last Train Steward card.
Don't need to upgrade any spell cards.
Take Tempered Talisman artifact if you can afford it.

Battle with Seraph

Turn 1
Bottom floor lineup: Champion -> Guard of the Unnamed
Use Energy Siphon on Seraph.
Use Urchin Spines on bottom floor.
Use Frozen Lance on bottom floor.
Use Sting on bottom floor.

Turn 2
Use Urchin Spines on top floor with Seraph.
Use Energy Siphon on Seraph.
Use Crypt Builder on Seraph.

The achievement should pop.

As previous guides for this achievement have been nerfed to a greater or lesser extent by the DLC, here is a simple way to get both Archus and Seraph before their combat phase.
Seed - StickyBufferLogos
Artifact - Lightstone Casing
Champion - Eternal Flame
Always try to kill your champion each turn to pump it up for the boss, especially in later rounds.
1st battle (The Gathered Clergy)- take subsuming blade, take left path and make it cost less and gain Holdover.
2nd battle (Pyre Absorbers) - take right path to get Waxer Snuffer and Bounty Stalker.
From now on, kill Bounty Stalker with Subsuming Blade at the first opportunity, bringing it back with Primitive Mold for this fight.
Talos - collect Rationing Scales and Fel's Remorse, take left path, upgrade Bounty Stalker with Multistrike, reroll and upgrade again with Endless. Start purging your Primitive Molds and choose Eternal Flame II on your Champion.
From now on, kill Bounty Stalker with Subsuming Blade at every opportunity, rinse and repeat.
4th Battle (Clipped Collectors) - take right path, make Subsuming Blade zero cost.
5th Battle (The Harpy's Guard) - take the left path and duplicate your Bounty Stalker, which should now be over 200*3 damage.
Archus - Bounty Stalkers on the top floor should do it on turn 2. Take the left path to purge a couple more Molds and upgrade your Champion to Eternal Flame III.
7th Battle (The Winged Horde) - take the trial. Take the right path and purge away your Imps and/or Guards, continuing to purge from the artifact screen.
Seraph - put your Bounty Hunters on the middle floor and get a first turn kill.

Not trying to step on the toes of the first guide. It is a great guide and will definitely get you the achievement. I'm just posting the continuation guide of the seed you can use to defeat Daedalus, Fel and Seraph before their battle phases in one go.

Input the following seed into the Community Challenges section:

StoreSurplusRates

Take the Glutton champion all the way through and pass on the starting artifacts to get the gold. For now the strategy is put your champion on the bottom floor and feed him morsels. Make sure you turn on every trial for every fight to maximize gold.

Turn on the trial for the first fight then only grab the Morselmaster after you beat the boss. Make sure you summon your champion first from now on then add the Morselmaster behind it or you will end up summoning 2 champions and have no room for morsels.

Take the left path to reduce the cost of Shadesplitter to 0, reroll and reduce another to 0 and add holdover.

Turn on the trial for level 3 then hang right to grab a 2nd Morselmaster.

I outlined how to use this build to defeat Daedalus before his battle phase under his achievement. After killing him take Overgorger and the card draw upgrade.

From here on out your main objective is to feed your Overgorger whenever possible, even before your champion. Put it on the top floor with a Morselmaster behind it.

Take the right path on level 4 to reduce your deck, getting rid of spells and grabbing the gold from the banner. Grab Mitosis after the fight.

Go right on level 5 to further reduce your useless spells. Now that you have Mitosis, put a morsel behind your Overgorger then hit it with the Mitosis to max out the floor.

Head left on level 7 to pick up the Fossilized Fangs artifact from the shop then use your gold to purge as many spells and conductors as possible, obviously keeping your Shadesplitters for morsel generation. You should have about 13 cards going into the boss fight.

Again, I am not sure about the RNG of card draws but the idea is to summon your Morselmaster on the top floor FIRST this time, then put your Overgorger in front, summoning 2. Then when Fel moves to the 3rd floor you should pull your Mitosis. Hit your Overgorger with it (or before if you draw it sooner) and you will fill the floor with Overgorger copies, crushing Fel. Take the card draw upgrade option.

Go left on 7 and grab the Abandoned Antumbra artifact. Make sure you turn on the trial for this fight to get that 400 extra gold.

Hang one last left on level 8 to ditch a couple more cards in the Vortex. Use the Merchant of Magic to reduce the cost on your Mitosis and spend the rest of your gold purging cards. You should have 6 or so cards left, leaving your champion, 1 Shadesplitter, 1 Mitosis, 2 Morselmasters and your Overgorger.

With luck you will pull a Morselmaster, your Overgorger and 0 cost Mitosis your first turn. Put the Morselmaster down on the same floor as Seraph, then your Overgorger in front of it and hit it with Mitosis. This should be enough to kill Seraph on your first turn.

Depending on draw RNG you may need to adjust which floor you set up on if you don't get all the cards you need first turn.

This should pop the Sans Seraph achievement.

Enjoy!