Valkyrie's Call, Amoeboid Changeling, Spawning Pit, and Great Oak Guardian

Prerequisites

• Valkyrie's Call on the battlefield
• Amoeboid Changeling on the battlefield
• Spawning Pit on the battlefield
• Great Oak Guardian on the battlefield

Steps

1. Activate Amoeboid Changeling's second ability by tapping it, removing all creature types from Great Oak Guardian
2. Activate Spawning Pit by sacrificing Great Oak Guardian
3. When Great Oak Guardian dies, Valkyrie's Call triggers, returning Great Oak Guardian from your graveyard to the battlefield as an Angel with flying and a +1/+1 counter on it
4. When Great Oak Guardian 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 untap of creatures you control
• Infinite mana creatures you control can produce
• Infinite charge counters on a permanent
• Infinitely large creatures you control until end of turn