Moxite Refinery + Magistrate's Scepter + Mossborn Hydra + Arid Archway

Moxite Refinery

Magistrate's Scepter

Mossborn Hydra

Arid Archway

How it works

1. Play Arid Archway. When it enters, it and Mossborn Hydra trigger.
2. Resolve the Arid Archway trigger, returning it from the battlefield to your hand.
3. Resolve the Mossborn Hydra trigger, doubling the number of +1/+1 counters on it.
4. Activate Moxite Refinery by paying 2, tapping it and removing three +1/+1 counters from Mossborn Hydra, putting three charge counters on Magistrate's Scepter.
5. Activate Magistrate's Scepter's second ability by tapping it and removing three charge counters from it, causing you to take an extra turn after this one.
6. Repeat each turn.