Slay the Spire: Guardian 45

[@kurorooo7360]

You can play as the bosses? What mode is this?

[@mernix]

It's a fan-made mod, available as an expansion to Slay the Spire on steam for free. Go try it :)
store.steampowered.com/app/1865780/Downfall__A_Slay_the_Spire_Fan_Expansion/