Acid blood is one of the 35 possible corruptions that can be inflicted on the PC. While in effect it provides immunity to all acid damage, and if a monster attacks the PC some acid can splash back on the monster (perhaps only if a bleeding wound is caused) — causing some damage and possibly even blinding it for a few turns (if not undead or a construct, or otherwise immune to being blinded). It is unknown if the corruption has any negative effects, e.g. slowing down HP regeneration