Ebonkoi

Corruption water is the only place these bite, so you either fish a natural chasm pool or dig your own pond inside the biome. Making one on the surface is safer than leaning over a chasm, and it works just as well as fishing deep.

Wrath is the payoff. It lifts your damage for a long stretch and stacks with everything else in a standard boss kit, so a stack of these becomes a flat damage bump across a whole tier of progression. Catch more than you think you need. Dying clears the buff, and a fight that takes four attempts eats four bottles.