Coretapper and Myr Galvanizer do not have summoning sickness.
({1} magic symbol) each turn available.
Steps
Activate Coretapper's first ability by tapping it, putting a charge counter on Magistrate's Scepter.
Activate Myr Galvanizer by paying ({1} magic symbol) and tapping it, untapping each other Myr you control.
Activate Coretapper's first ability by tapping it, putting a charge counter on Magistrate's Scepter.
At the beginning of combat on your turn, Urtet triggers, untapping each Myr you control.
Activate Coretapper's first ability by tapping it, putting a charge counter on 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.