Champion Belt

Champion Belt is a rare relic that applies 1 additional Vulnerable whenever you apply Vulnerable to any enemy. So if you apply 1 Vulnerable to an enemy, they instead receive 2 Vulnerable. Vulnerable causes enemies to take 50% more damage from attacks (75% with Paper Phrog), and extra stacks increase its duration.

Champion Belt dramatically extends the uptime of Vulnerable on enemies. With double stacks applied each time, enemies stay Vulnerable for twice as many turns, meaning more of your attacks hit them while they're amplified. It pairs powerfully with Bag of Marbles (free Vulnerable at combat start, doubled to 2 by Champion Belt) and Paper Phrog (which increases Vulnerable's multiplier). In builds with multiple Vulnerable-applying sources, Champion Belt ensures enemies are almost permanently Vulnerable throughout a fight.