What a coincidence! Last night I was thinking I'm starting to get tired of Slay the Spire and here comes a new roguelite deck-builder:
The premise is an apocalyptic war has resulted in Hell's near-defeat, with the result that hell has literally frozen over. You and your band of demons have one of the few remaining crystals of hellfire that if returned to the center of Hell can reignite the whole netherworld. So you and your demons load up on a four-story-tall demonic train and make for the center while fending off angelic attack.
Like Slay the Spire it's a deckbuilder where you start out with a deck of trash cards and as the game goes on there's an equal emphasis on gaining new more powerful cards and removing the trash cards to make it more likely to draw the power cards when you need them.
Each battle you place monsters on one of four levels of the train and enchant them with various synergies. Each round several angelic enemies enter the bottom floor and exchange attacks with your demons on the same floor. If any angels survive, they ascend to the second floor and fight your defenders there for a round. If an angel gets to the fourth floor, it exchanges blows with your hellfire crystal until they die or the crystal is destroyed (which loses the game).
A playthrough is shorter than a game of Slay the Spire, and it's much more forgiving for beginners (after a couple aborted early attempts I cleared my first full run at bottom difficulty) but the game hints at much higher difficulties to unlock. There's also barely any tutorial in the game. One thing I REALLY appreciate is this game gives you a full preview of the 3 main bosses and all their special powers before you make a single decision so you don't, say, go with a shiv-based build, unaware that the time-eater is waiting on floor 3.
I wouldn't say it's a replacement for Slay the Spire, as demons stay in place after you put them down and attack automatically, giving it more of a magic the gathering feel than a card-based blobber RPG. It also has unique features like a "hero" monster card that can be played for free and unlocks new abilities from various skill trees as the game goes on.