Vampire

Exhaustion Level Time Effects Blood needed
1 3rd day without blood Disadvantage on Ability Checks 4 HP
2 4th Speed halved 6 HP
3 5th Disadvantage on attack rolls and saving throws 8 HP
4 6th Hit Point Maximum Halved 10 HP
5 7th Speed reduced to 0 12 HP
6 8th Death 14 HP

If you drink 2 HP worth of blood, you can set your exhaustion back a level till your next long rest.
If you reach Exhaustion Level 6, make a constitution saving throw. If you succeed, you gain another hour to live, if you fail, you die instantly. You get three chances at this, with increasing DC. On your first attempt, you have to succeed against a DC of 10, on second, against 15 and on the last against 20.