Valkyrie's Call, Amoeboid Changeling, Spawning Pit, and Corridor Monitor

Prerequisites

• Valkyrie's Call on the battlefield
• Amoeboid Changeling on the battlefield
• Spawning Pit on the battlefield
• Corridor Monitor on the battlefield

Steps

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

Results

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