Gravespawn Sovereign, Intruder Alarm, and Ashnod's Altar

Prerequisites

• Gravespawn Sovereign on the battlefield
• Intruder Alarm on the battlefield
• Ashnod's Altar on the battlefield
• You control at least four other Zombies and an additional nontoken creature

Steps

1. Activate Ashnod's Altar by sacrificing a nontoken creature, adding
2. Activate Gravespawn Sovereign by tapping five untapped Zombies you control, returning any creature from your graveyard to the battlefield
3. The creature enters the battlefield, triggering Intruder Alarm, untapping all creatures
4. Repeat

Results

• Infinite colorless mana
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers
• Infinite untap of creatures