First Day of Class, and Yahenni, Undying Partisan

Prerequisites

• First Day of Class in hand
• Yahenni, Undying Partisan on the battlefield
• available

Steps

1. Cast First Day of Class by paying
2. Activate Yahenni by sacrificing the persist creature
3. When the persist creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
4. When the persist creature enters, First Day of Class triggers, putting a +1/+1 counter on the persist creature
5. Resolve the Yahenni ability
6. Repeat from step 2

Results

• Infinite ETB
• Infinite LTB
• Infinite death triggers
• Infinite sacrifice triggers