Hellkite Charger + Shriekwood Devourer

Hellkite Charger

Shriekwood Devourer

How it works

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.
5. Resolve the Hellkite Charger trigger, causing you to pay 5 to untap all attacking creatures you control and causing you to get an additional combat phase after this one.
6. Repeat.