Blightbeetle + Altar of Dementia + Harmless Offering

Blightbeetle

Altar of Dementia

Harmless Offering

How it works

1. Donate Blightbeetle to an opponent
2. Activate Altar of Dementia by 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. Resolve the Altar of Dementia ability.
5. Repeat from step 2.

This clever setup uses Harmless Offering to saddle an opponent with Blightbeetle, turning the beetle's passive stance against +1/+1 counters into your greatest asset. Once your opponent is guarding that restriction, you can repeatedly cycle your undying creature into Altar of Dementia for infinite sacrifices. Because Blightbeetle prevents counters from being placed on opponents' creatures, the undying trigger completely ignores its usual penalty, returning the creature to the battlefield unblemished and ready to be fed to Altar of Dementia all over again.