Vampirism is one of the many legacies available in the Legends Mod. It is currently, however, the only legacy belonging to the Horror part of the mod.
In the Mod
Vampirism can be accessed through the Altar. The legacy can be acquired with the vampirism infection. To get this infection you will need to get bitten by a Vampire while holding a Vampire Totem. Once you have been infected, you can enable the vampire legacy in the Altar.
Instead of regular food, vampires need blood to regain their food bars. As a vampire, you can see how much blood you have in their blood meter on the bottom right-hand corner of your screen. Vampires can drink blood straight from a mob or player, or they can drink Bottles of Blood.
As a vampire you have a wide selection of different abilities which can be unlocked in the Altar. Vampires can level up by unlocking all of the abilities which belong to your level in exchange for experience levels.
Vampires will take damage from sunlight. This can be avoided by simply wearing a helmet, or standing below a block to block out the sunlight.