Intruder Alarm, Deeproot Pilgrimage, and Firdoch Core

Prerequisites

• Intruder Alarm on the battlefield
• Deeproot Pilgrimage on the battlefield
• Firdoch Core on the battlefield
• available

Steps

1. Activate Firdoch Core's first ability by tapping it, adding one mana of any color
2. Deeproot Pilgrimage triggers
3. Holding priority, activate Firdoch Core's second ability by paying , causing it to become a 4/4 artifact creature until end of turn
4. Resolve the Deeproot Pilgrimage trigger, creating a 1/1 Merfolk creature token
5. When the Merfolk enters the battlefield, Intruder Alarm triggers, untapping all creatures
6. Activate Firdoch Core's first ability by tapping it, adding one mana of any color
7. Deeproot Pilgrimage triggers, creating a 1/1 Merfolk creature token
8. Repeat from step 4

Results

• Infinite ETB
• Infinite colored mana
• Infinite creature tokens
• Infinite mana creatures you control can produce
• Infinite untap of creatures