Spark Double + Puppeteer Clique + Altar of Dementia

Spark Double

Puppeteer Clique

Altar of Dementia

How it works

1. Cast Spark Double, choosing to have it enter as a copy of Puppeteer Clique.
2. Resolve its ETB trigger.
3. Sacrifice it to Altar of Dementia targeting an opponent.
4. Persist triggers, returning Spark Double with a -1/-1 counter, which is removed because of the +1/+1 counter that Spark Double enters with.
5. Repeat to get every creature out of each opponent library and mill them all out.