Bag of Marbles

Bag of Marbles is a common relic that applies 1 Vulnerable to all enemies at the start of every combat. Vulnerable causes affected enemies to take 50% more damage from attacks (or 75% more with Paper Phrog). Because it hits all enemies simultaneously and requires no energy or cards, it essentially multiplies your first turn's offensive output in every single fight.

The relic is broadly strong across all characters but scales best in burst damage builds. On turn 1, every attack you play already benefits from the Vulnerable debuff, meaning you effectively get 50% more damage from your entire first turn of attacks without spending any resources. In multi-enemy rooms the bonus applies to all targets at once. Bag of Marbles also synergizes with Champion Belt (which adds another Vulnerable stack) and any deck that wants to end fights quickly on the first or second turn.