Monster Train

Input the following seed into the Community Challenges section.

InfectedCabinetsFederal

Start with the Cultivating champion for the +1 card draw and grab the Improved Firebox artifact.

Turn on the trial for the first fight and pick up the Siren of the Sea monster. Take the left path for the gold and to decrease one of your Frozen Lances to 0 cost.

Early game strategy is to put the Siren behind your champion and cast as many spells as possible to pump her.

Grab Restoration Detonation from the second fight and head left again to add 10 magic power to it at the Merchant of Magic. You can give the guy in the ice cave a unit just to keep it out of your deck for a few fights.

Definitely get the Lodestone Totem after defeating Daedalus. This is probably the most OP card in the game. Go with the capacity upgrade so everyone outside your conductors can fit on one row and switch to the Explosive champion upgrade now that your champion will no longer be taking any significant damage.

I would head right after this fight to start thinning down your deck. Don't blow all your gold just yet as you'll want to buy an artifact later on.

If you are going for maximum points you can turn on the trial for the level 4 fight which gives a useful artifact, you can also take the Restoration Retreat to ensure you always have your units on the bottom floor even when they won't fit but it is not necessary for the build.

Take the right path on level 5 and reroll the Merchant of Steel to add multistrike to your Siren.

On level 6 use the Unstable Vortex to thin out your conductors.

After you beat the boss Archus, upgrade your card draw. Take the left path to grab the Forever Flame from the random trinket box and then Winged Steel from the shop.

Turn on the trial for the level 7 fight to get that sweet 400 gold which you'll use to thin out cards before the final boss.

Take the left path and put another multistrike on your Siren then purge any remaining non-healing cards you can using the Vortex and merchant. Ideally you should have about 7-8 spells left.

Boss strategy is pretty straightforward. Place everyone on the same floor and cast spells like crazy. You'll need to put everyone on the second floor because they will not fit on the first. If going for points, you can decend the Edge Prior using the Restoring Retreat to get everyone on the first floor.

This can unlock the Win at Covenant 5, 10, 15 and 25 achievements if you do not have them already as well as The Awoken.

Enjoy!

There's a much easier way to get this. Create your own challenges!

Set the challenge to Covenant 25, select the Dante mutator with either the two Purge card mutators, or one purge and the quick mutator. Dante gains 1 multistrike for every purge card in your deck so you want as many as possible. Upgrade Dantes attack throughout the run (getting quick if you didn't choose the mutator) and duplicate him as often as you can (ideally after he has quick) and grab the additional floor space after the first boss.

Don't take any additional trials that involve spikes unless you really want to as they're the only thing outside of bosses that really damage Dante. With average luck you can get 4 Dantes by the end of the run, each doing about 30 x 11 damage per turn, more if you get some good luck at the Merchant of Steel. NOTE: If you get the cavern event for the Excavated Ember purge cards, DO NOT TAKE THEM, when they upgrade, all of them upgrade drastically reducing your multiplier.

I don't know if you can duplicate Dante without the DLC, but if not, duplicate the purge cards.