Mighty Mutanimals, Devoted Druid, and Hapatra, Vizier of Poisons

Prerequisites

• Mighty Mutanimals on the battlefield
• Devoted Druid on the battlefield
• Hapatra, Vizier of Poisons on the battlefield

Steps

1. Activate Devoted Druid's first ability by tapping it
2. Activate Devoted Druid's second ability by putting a -1/-1 counter on it
3. Hapatra triggers, creating a creature token
4. When the creature token enters, Mighty Mutanimals triggers, putting a +1/+1 counter on Devoted Druid
5. Resolve the Devoted Druid ability from step 2, untapping it
6. Repeat

Results

• Infinite ETB
• Infinite creature tokens
• Infinite green mana