Viper Bottle

A rare single-use consumable with a painful price tag: drink it and take 5 damage, but permanently gain +1 to a random stat. The stat boost sticks for the entire run, making Viper Bottle one of the few items that directly improves your character long-term. Which stat you get is random, so it’s always a gamble. The wiki also notes it may have unspecified side effects beyond the stated damage. Worth using when you can spare the HP cost, especially early in a run when permanent gains have the most impact.