Tainted Observer, Ashnod's Altar, and Scurry Oak

Prerequisites

• Tainted Observer on the battlefield
• Ashnod's Altar on the battlefield
• Scurry Oak 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 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