These buffs would be made possible through a time and resource intensive witchcraft ritual of some sort. Lasts forever unless the user finds a cure (if they choose to). Would be spread through certain interaction with such people.
Lycanthrope:
-Unlocks skill Lycanthropy
-Unlocks available Lycanthrope-only skill tree
-Biles are increased by 10%
-Unnarmed combat damaged increased significantly
-Player with Lycanthropy is dealt 50% more damage from silver weapons and musketballs
-Lycanthropes turn into Werewolves during a Blood Moon
-Werewolves have 25% increase in biles
-Surviving combat with a Werewolf has a chance to turn a player into a Lycanthrope after the Blood Moon
Vampires:
-Unlocks skill Vampirism
-Unlocks Vampire only skill tree
-Biles increased by 20%
-Cannot travel outside of darkness without a special debuff
-Can feast on players in beds to regen biles
-Players who are feasted on will become Vampires
-Vampires cannot feast on other Vampires
-Vampires cannot feast on a player wearing a Garlic Charm or holding a Crucifix in their left hand
-Vampires take significantly more damage from players wielding a Crucifix or using Steel Weapons
-Vampires that go out of darkness with no debuff will experience a harsh bile drain, and will Permadie if they KO
Any more suggestions may be added in this thread!