The Time Eater

Defeat the Time Eater, one of the three Act 3 bosses (with The Shapes Donu & Deca and The Crow the Awakened One). Every 12 cards you play it ends your turn, so it hard-counters high card-count and infinite decks - play fewer, bigger cards and don't waste plays. At half HP it heals and gains Strength, so try to burst through that threshold rather than stall. Down to Act 3 boss RNG.