Monster Train

Probably a whole bunch of menthods to get this, but since there is no guide I'll share how I got the achievement.
I'm no expert in this game, so can't give you any free genius strategy on this one. But hopefullt this can get you headed in the right direction.

You'll want to start a new run with Mutators. For ease, you can do this without any covenant.
First mutator you definately need is Fallen Champion as this removes the champion card and lets you go for the achievement. Basically you need to win a run with this mutator on.
Next, pick two other mutators that will help you out. I went with Hastag Blessed for extra artifacts, and Burn Bright for more ember each turn.

Next you'll want to think about what clans to use. You won't have a champion, so think about your tactics regarding how you can beef up the regular units.
I went with Melting Remnant as my main clan and took the Primitive Mold starter cards. The idea being that I would be Reforming a lot of units when they died or burned out, and going for artifacts and abilities that had them come back stronger. (I had two artifacts turn up that made death strats stronger, the Resin and the snuffer, and struggled to find units that had good extinguish abilities)
Even with some admittedly pretty poor execution, I was able to just about get the win. I think if more death and reform bonuses had shown up in the run it would have been easier for me. In the end, Bounty Stalker was a life saver (he gets permanent +8 damage on every death), by the end of the run he had 146 damage and I duplicated him in a hell vent.

If you want to try other methods, I would say look for units with some trigger ability that you can exploit a lot. A few ideas I haven't tried but you could have a go at.
- Hellhorn with endlessly stacking armor and rage could work.
- Awoken deck built around big HP units and stacking spikes
- Umbra morsel deck and units with gorge abilities - Overgorger could get OP

With the DLC enabled, I made a challenge that will easily net you this. It just requires a few precise steps. You may play as you like as long as you follow these outlines.

PLEASE NOTE - You will have a few rocky levels where you cannot purge cards that hurt your pyre. This is okay. You will be in no danger, we start with 80 pyre health and after area 4-5 it won't matter anymore.

ALSO NOTE - Dante will ALWAYS be in the front of a row, unless you notice on turn one it would let him die, then you place somebody in front of him. As soon as he gets stronger it won't matter but many times the beginning of combat will make or break your run.

MailedMobilesCowboy

You primary Umbra, with a secondary of Awoken.
You start with Dante and 8 calcified embers, each which grant additional multi-strike. Obviously you also start without a champion.

Any time you get a card reward, if it isn't to create a morsel, to create a morsel maker, to get an item like Rootseeds or Razor Edge to increase attack, OR an umbra unit that has a gorge ability, we rarely want it.

Pre area - Take the artifact (Winged Technology) for morsel shield. Accept the challenge for the unit draft. Place Dante on the TOP row of the train and feed him morsels. If you begin your turn and you notice a red X over his life and armor, he will die, so place something in front of him. This is why our morsels need shield.
When you win, your item draft will be the Morsel Maker. He will always be behind a Dante.

Area 1 - Go to the steel merchant and purchase "Quick" for Dante. You won't have the money for anything else. Again, Dante will fight on the top row, and from here on out, we avoid challenges no matter the reward, and we avoid caverns as we don't want to lose our calcified embers.
Our Umbra unit here will gain be a Morsel Maker. Same as above.

Area 2 - Go to the steel merchant and purchase +10 attack power for Dante. The reroll won't help us here. This is one of the last times Dante needs to be on the top row. Remember, we are going for an achievement, not letting our train survive for score.

After the first boss you want Light of Seraph for the floor capacity.

You will notice Hell vents to duplicate cards going forward. These we will want to use on Dante. You get the next two very quickly after this.

After the second boss you want Fels remorse for the +1 ember per turn.

You will face few difficulties at this point. I was killing bosses before their attack phase (including the final boss)

Area 7, however, has an artifact merchant. Reroll if you don't want any other artifacts (KEEP AT LEAST 240 GOLD) as it will net us (Commemorative Spike) which gives us a Morsel Miner on each floor, that gives 6 health and damage.

Area 8 Will have bottom floor Dante die if somebody is not in front of him, so place any units you can to take the hits. We want to feed the other two Dante units. This area is why we wanted extra Ember a turn.

If you followed these outlines you will get this achievement with relative ease. If you have any questions, please ask me and I will tell you any further details you need.

Happy hunting (>*_*)>