Time Sieve + Myr Battlesphere + Debtors' Knell

Time Sieve

Myr Battlesphere

Debtors' Knell

How it works

1. At the beginning of your upkeep, Debtors' Knell triggers, returning Myr Battlesphere from your graveyard to the battlefield.
2. Myr Battlesphere enters the battlefield, creating four 1/1 Myr artifact creature tokens.
3. Activate Time Sieve by tapping it, sacrificing Myr Battlesphere and the four Myr tokens, causing you to take an extra turn after this one.
4. Repeat each turn.