Tainted Observer + Ashnod's Altar + Scurry Oak

Tainted Observer
Ashnod's Altar
Scurry Oak

Requires
Tainted Observer must be on the battlefield. Ashnod's Altar must be on the battlefield. Scurry Oak must be on the battlefield. You have a way to cause a creature to enter the battlefield under your control. Scurry Oak has at least one +1/+1 counter on it.
Steps
  1. Cause a creature to enter the battlefield under your control.
  2. When the creature enters the battlefield, Tainted Observer triggers.
  3. Holding priority, activate Ashnod's Altar by sacrificing the creature, adding .
  4. Resolve the Tainted Observer trigger, causing you to pay 2 to put a +1/+1 counter on Scurry Oak.
  5. Scurry Oak triggers, creating a 1/1 Squirrel creature token.
  6. Repeat from step 2.
Results
Infinite +1/+1 counters on Scurry Oak. Infinite death triggers. Infinite ETB. Infinite LTB. Infinite proliferate. Infinite sacrifice triggers.

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