Swarm Shambler is a rare Creature — Fungus Beast card from Magic Online Promos (PRM), collector number 83740.
This creature enters with a +1/+1 counter on it. Whenever a creature you control with a +1/+1 counter on it becomes the target of a spell an opponent controls, create a 1/1 green Insect creature token. {1}, {T}: Put a +1/+1 counter on this creature.