At the beginning of your upkeep, Debtors' Knell triggers, returning Coretapper from your graveyard to the battlefield.
Activate Coretapper's first ability by tapping it, putting a charge counter on Magistrate's Scepter.
Activate Coretapper's second ability by sacrificing it, putting two charge counters 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.