Priest of Urabrask does not have summoning sickness.
You have at least three opponents.
An opponent is unable to block and kill Priest of Urabrask and Hellkite Charger.
Steps
Declare Priest of Urabrask as an attacker.
Hellkite Charger and Priest of Urabrask' myriad ability trigger.
Resolve the Priest of Urabrask trigger, creating at least three token copies of it that are tapped and attacking.
The Priest of Urabrask tokens enter the battlefield, adding at least nine ({R} magic symbol) .
Resolve the Hellkite Charger trigger, causing you to pay ({5} magic symbol) ({R} magic symbol) ({R} magic symbol) to untap all attacking creatures you control and to get an additional combat phase after this one.
At the end of your combat phase, Blade of Selves triggers, exiling the Priest of Urabrask tokens.