The potion of blood and potion of vampire blood are SLASH'EM specific items. They are primarily of interest to Vampire players. Dipping a unicorn horn into a potion of (vampire) blood will turn it into water, which is typically the only use for non-vampires. Despite being potions, drinking either potion will break vegetarian conduct. A thrown potion of (vampire) blood that lands on a non-chaotic altar will convert the altar to chaotic and abuse your wisdom, even if you are chaotic. This will anger an attendant priest, but has no other effects.
Potion of Blood Edit
A vampire can drink a potion of blood to gain 30 nutrition if blessed or 20 if uncursed, halved if the potion is diluted. Cursed blood has congealed and will give 0 nutrition. Non vampires that drink the potion will vomit for 10d8 (more) turns.
Potion of Vampire Blood Edit
A vampire player can drink a noncursed potion of vampire blood to gain 400 nutrition points. If the potion is blessed, your HP and max HP will be increased by the same amount as from a level gain. Vampire monsters can make use of this potion to heal themselves for d8 + d2 hit points if not cursed ("Monster looks full of life."). If the potion is cursed there is no effect ("Monster discards the congealed blood in disgust."). This will identify the potion if it is seen. If a non-vampire player drinks the potion, they will polymorph into a vampire and abuse their constitution. Note that the resulting polymorph is semi-permanent -- it has no timeout, but you will revert back to your normal form if your HP are drained to zero. Neutral characters will suffer a -3 alignment penalty, while lawful characters and monks will suffer a -15 alignment penalty and anger their god.
Neither potion is randomly generated. Vampire players playing as a role that normally starts with food will receive potions of vampire blood instead. Potions of vampire blood can be created by a player vampire using the draw blood technique if the player also has a medical kit with phials. Finally, vampires, vampire lords, and vampire mages have a 50% chance of being generated with a potion of either blood or vampire blood; there is a <level> in 30 chance that the potion will be vampire blood, otherwise it is regular blood. Because enemy vampires will drink potions of vampire blood to heal themselves, it is important for player vampires to kill them quickly to avoid losing the potion. Fire vampires and star vampires do not start with potions of blood, but can make use of any they find on the ground.