Gravewaker + Coretapper + Magistrate's Scepter

Gravewaker

Coretapper

Magistrate's Scepter

How it works

1. Activate Coretapper's first ability by tapping it, putting a charge counter on Magistrate's Scepter.
2. Activate Coretapper's second ability by sacrificing it, putting two charge counters on Magistrate's Scepter.
3. Activate Magistrate's Scepter's second ability by tapping it and removing three charge counters from it, taking an extra turn after this one.
4. Activate Gravewaker by paying 5, returning Coretapper from your graveyard to the battlefield tapped.
5. Repeat each turn.