Next time your PC would his 0 hp instead you will be revived with 1 hp. Once this effect triggers progress vampirism by one stage (You will get the effects of all previous stages). This effect my occur once per 2d4 long rest.
Stage 0 (characters before being revived by this feat): gain dark vision 60ft or 120 ft if you already had dark vision.
Stage 1: Your vampiric blood starts pumping through your veins you now have “Sunlight Sensitivity”- While in direct sunlight, the PC has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight. You also gain “undead armour” -while NOT wearing heavy armour your armour class is raised by 3.
Stage 2: Your body becomes more undead with each feign death you now gain Damage Resistances to Necrotic; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks. Sunlight sensitivity increases and you will now take radiant damage equal to your hit die for any short or long rest taken in sunlight.
Stage 3: Your vampiric powers grow but so does your hunger you gain the ability to “Bite” - Melee Weapon Attack: +9 to hit, reach 5 ft., one willing creature, or a creature that is grappled by the vampire, incapacitated, or restrained. Hit: 7 (1d6 + 4) piercing damage plus 10 (3d6) necrotic damage. The target''s hit point maximum is reduced by an amount equal to the necrotic damage taken, and the vampire regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. A humanoid slain in this way and then buried in the ground rises the following night as a vampire spawn You must make a charisma check (DC 18) to see if the spawn will obey you or try to destroy you.