Rage Potion

It is flat critical strike chance across every damage type that can crit. Summon weapons cannot, so a pure summoner drinking this gets nothing at all and should spend the buff slot elsewhere. For everyone else it is one of the standing boosts you want up before you swing a boss summon.

The Wrath Potion is the corruption side of the same idea and raises damage instead of crit. They occupy separate buff slots, so a well stocked player runs both and does not have to pick.

This normally comes out of crimson water, which a corruption world does not have. You can force it: the Dryad sells Crimson Seeds once a hardmode graveyard is set up around her, and a patch of planted crimson big enough to fish in behaves like the real biome.