Crypt Ghoul

Deadly Infection. When hit by a Bite attack the  target must make a constitution saving throw dc12. On its 1st failed save the targets speed is halved, on a 2nd the targets vision is halved, on a 3rd the target rolls attacks with disadvantage, on a 4th the target falls prone, on a 5th the target falls unconscious. On every successful save the targets goes back to the previous level of infection. After becoming infected the target makes a con save at the end of their turn, this is still rolled if the target is unconscious. Outside of combat the infected target must take a short rest to recover from their infection, make a medicine check dc12 to cure the infection or use a healing spell or potion. Neglecting to do this will cause the infection to worsen every hour. 

Cowardly. Crypt Ghouls attack in numbers or not at all. If their numbers are ever depleted below a quarter they will flee.

Claws. Melee Attack: +2 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 3) slashing damage. 

Bite. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 3) piercing damage.