Coretapper + Magistrate's Scepter + Debtors' Knell + Lightning Greaves

Coretapper

Magistrate's Scepter

Debtors' Knell

Lightning Greaves

How it works

1. At the beginning of your upkeep, Debtors' Knell triggers, returning Coretapper from your graveyard to the battlefield.
2. Activate Lightning Greaves' equip ability by paying 0, attaching it to Coretapper.
3. Activate Coretapper's first ability by tapping it, putting a charge counter on Magistrate's Scepter.
4. Activate Coretapper's second ability by sacrificing it, putting two 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.