Mirko, Obsessive Theorist + Coretapper + Magistrate's Scepter + Hex Parasite

Mirko, Obsessive Theorist

Coretapper

Magistrate's Scepter

Hex Parasite

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, causing you to take an extra turn after this one.
4. At the beginning of your end step, Mirko's last ability triggers, returning Coretapper from your graveyard to the battlefield with a finality counter on it.
5. Activate Hex Parasite by paying 1B/P, removing the finality counter from Coretapper and giving Hex Parasite +1/+0 until end of turn.
6. Repeat each turn.

This brilliant engine achieves infinite turns by repeatedly recycling Coretapper to continually charge up Magistrate's Scepter. Since Coretapper returns to the battlefield with a pesky finality counter from Mirko, Obsessive Theorist's end step trigger, Hex Parasite elegantly swoops in to consume that counter for a minimal life or mana payment, allowing Coretapper to safely die and repeat the cycle on the next turn.