Hydra Flail

This flail's spiked head is held in the jaws of a metal hydra figurehead. Whenever you score a critical hit with this weapon against a hostile creature, the weapon magically grows another spiked head. You gain a +2 bonus to damage rolls made with this magic weapon for each head the flail has (to a maximum of +6). After 1 hour, any head the flail grows in this way falls off and disappears.