Magistrate's Scepter + Coretapper + Contagion Engine

Magistrate's Scepter

Coretapper

Contagion Engine

How it works

1. Activate Coretapper's first ability by tapping it, putting a charge counter on Magistrate's Scepter.
2. Activate Contagion Engine by paying 4 and tapping it, proliferating twice, putting two additional charge counters on Magistrate's Scepter.
3. Activate Magistrate's Scepter's second ability by tapping it and removing three charge counters from it, taking an extra turn after this one.
4. Repeat each turn.