Blightbeetle + Blasting Station + Zedruu the Greathearted

Blightbeetle

Blasting Station

Zedruu the Greathearted

How it works

1. Donate Blightbeetle to an opponent
2. Activate Blasting Station by tapping it and sacrificing the undying creature.
3. When the undying creature dies, its undying ability triggers, returning itself from your graveyard to the battlefield without a +1/+1 counter on it due to Blightbeetle.
4. When the undying creature enters, Blasting Station triggers, untapping Blasting Station.
5. Resolve the Blasting Station ability from step 2.
6. Repeat from step 2.

To pull off this insidious little loop, you first use Zedruu the Greathearted to hand Blightbeetle over to your opponent, turning their side of the board into a graveyard for +1/+1 counters. With that restriction locked in place by Blightbeetle's passive text, you can feed an undying creature repeatedly into Blasting Station. Because Blightbeetle prevents those counters from ever being placed, the creature's undying ability keeps bringing it back fresh. Every time it drops back onto the battlefield, Blasting Station untaps itself to ready another shot of damage, letting you machine-gun your opponents down to zero.