Hellkite Charger + Druids' Repository

Prerequisites

You control at least six other creatures that can attack this turn. An opponent is unable to block and kill your creatures.

Steps

1. Declare Hellkite Charger and six other creatures you control as attackers, triggering Druids' Repository seven times and Hellkite Charger.
2. Resolve all Druids' Repository triggers, putting seven charge counters on it.
3. Activate Druids' Repository seven times by removing seven charge counters from it, adding {5}{R}{R}.
4. Resolve the Hellkite Charger trigger, causing you to pay {5}{R}{R} to untap all attacking creatures you control and to get an additional combat phase after this one.
5. Repeat each combat phase.