Hellkite Charger, and Shriekwood Devourer

Prerequisites

• Hellkite Charger on the battlefield
• Shriekwood Devourer on the battlefield
• You control up to seven lands that can tap to produce at least
• You control a creature with power 7 or greater that does not have summoning sickness, and that cannot be blocked and killed by an opponent

Steps

1. Declare any creature with power 7 or greater that cannot be blocked and killed by an opponent and Hellkite Charger if it isn't the aforementioned creature as attackers
2. Shriekwood Devourer and Hellkite Charger trigger
3. Resolve the Shriekwood Devourer trigger, untapping at least seven lands
4. Holding priority, activate up to seven lands by tapping them, adding at least
5. Resolve the Hellkite Charger trigger, causing you to pay to untap all attacking creatures you control and causing you to get an additional combat phase after this one
6. Repeat

Results

• Infinite ETB
• Infinite combat phases
• Infinite mana lands you control can produce
• Infinite untap of lands you control