Moxite Refinery + Magistrate's Scepter + Mossborn Hydra + Dimir Aqueduct

Moxite Refinery

Magistrate's Scepter

Mossborn Hydra

Dimir Aqueduct

How it works

1. Play Dimir Aqueduct. When it enters, it and Mossborn Hydra trigger.
2. Resolve the Dimir Aqueduct 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.