Valkyrie's Call, Amoeboid Changeling, Spawning Pit, and Little Bear

Prerequisites

• Valkyrie's Call on the battlefield
• Amoeboid Changeling on the battlefield
• Spawning Pit on the battlefield
• Little Bear on the battlefield

Steps

1. Activate Amoeboid Changeling's second ability by tapping it, removing all creature types from Little Bear
2. Activate Spawning Pit by sacrificing Little Bear
3. When Little Bear dies, Valkyrie's Call triggers, returning Little Bear from your graveyard to the battlefield as an Angel with flying and a +1/+1 counter on it
4. When Little Bear enters the battlefield, it triggers, untapping Amoeboid Changeling
5. Resolve the Spawning Pit ability, putting a charge counter on it
6. Repeat

Results

• Infinite ETB
• Infinite LTB
• Infinite charge counters on a permanent
• Infinite death triggers
• Infinite sacrifice triggers