Magistrate's Scepter + Lithoform Engine + Karn's Bastion + Doubling Season

Magistrate's Scepter

Lithoform Engine

Karn's Bastion

Doubling Season

How it works

1. Activate Karn's Bastion's second ability by paying 4 and tapping it.
2. Holding priority, activate Lithoform Engine's first ability by paying 2 and tapping it, copying Karn's Bastion's ability.
3. Resolve both Karn's Bastion abilities, putting four charge counters on Magistrate's Scepter.
4. 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.
5. Move to your next turn.
6. Activate Karn's Bastion's second ability by paying 4 and tapping it, putting two charge counters on Magistrate's Scepter.
7. Repeat steps 4 and 5 one time.
8. Repeat from step 1.