Putrid Goblin + First Day of Class + Clickslither

Putrid Goblin

First Day of Class

Clickslither

How it works

1. Cast First Day of Class by paying 1
2. Activate Clickslither by sacrificing Putrid Goblin
3. When Putrid Goblin dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
4. When Putrid Goblin enters, First Day of Class triggers, putting a +1/+1 counter on Putrid Goblin.
5. Resolve the Clickslither ability.
6. Repeat from step 2

This clever loop turns Clickslither into an infinitely large threat by exploiting the interaction between persist and counter-cancellation. When you sacrifice Putrid Goblin to Clickslither, its persist ability normally brings it back with a -1/-1 counter, but First Day of Class simultaneously steps in to place a +1/+1 counter on it the moment it enters the battlefield. State-based actions then cause the +1/+1 and -1/+1 counters to annihilate each other, leaving the goblin clean of counters and ready to be sacrificed all over again.