Blood Parasite

Lifelink
Whenever another nontoken creature dies, put
a +1/+1 counter on Blood Parasite. This ability
only triggers once per turn.
Remove a +1/+1 counter from Blood Parasite:
Create a 1/1 black Worm creature token with
lifelink. Activate this ability only if there is a
Plague token on the battlefield, and only
once per turn.