Coretapper + Magistrate's Scepter + Tezzeret the Seeker

Coretapper

Magistrate's Scepter

Tezzeret the Seeker

How it works

1. Activate Coretapper's first ability by tapping it, putting a charge counter on Magistrate's Scepter.
2. Activate Magistrate's Scepter's first ability by paying 4 and tapping it, putting a charge counter on it.
3. Activate Tezzeret's first loyalty ability by putting a loyalty counter on it, untapping Coretapper and Magistrate's Scepter.
4. Activate Coretapper's first ability by tapping it, putting a charge counter 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.