Activate Magistrate's Scepter's first ability by paying 4 and tapping it.
Holding priority, activate Lithoform Engine's first ability by paying 2 and tapping it, copying Magistrate's Scepter's ability.
Resolve both Magistrate's Scepter abilities, putting four charge counters on it.
Activate Manifold Key's first ability by paying 1 and tapping it, untapping Magistrate's Scepter.
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.
Move to your next turn.
Activate Magistrate's Scepter's first ability by paying 4 and tapping it, putting two charge counters on it.