Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Geralf's Mindcrusher + Yahenni, Undying Partisan

Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight

Geralf's Mindcrusher

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Geralf's Mindcrusher
2. When Geralf's Mindcrusher dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. When Geralf's Mindcrusher enters, it triggers, causing a player to mill five cards.
4. Activate Yahenni by sacrificing Geralf's Mindcrusher
5. When Geralf's Mindcrusher dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
6. When Geralf's Mindcrusher enters, it triggers, causing a player to mill five cards.
7. Resolve both Yahenni abilities from step 1 and 4.
8. Repeat.

This loop turns Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight into a cyclical engine by granting Geralf's Mindcrusher the persist ability it needs to alternate with its native undying. Whenever Yahenni, Undying Partisan sacrifices Geralf's Mindcrusher, the creature returns with alternating counters that continually cancel each other out, resetting its eligibility for both resurrection triggers. Every iteration forces a target player to mill five cards while triggering Yahenni, Undying Partisan's growth and sacrifice effects indefinitely.