Agonizing Parasites

Lifelink
When Agonizing Parasites is destroyed, it
becomes an enchantment and is exiled instead
of going to the graveyard. It returns to the
battlefield at the beginning of the next end step,
attaching to a target creature on the battlefield
as an enchantment aura.
When Agonizing Parasite is an enchantment aura,
it gives a -1/-1 counter to the creature to which
it is attached at the beginning of the enchanted
creature's controller's upkeep.