Mirrorweave by paying ({2} magic symbol) ({WU} magic symbol) ({WU} magic symbol) , causing each other creature to become a copy of
It That Betrays until end of turn.
Sacrifice
Bronze Bombshell by any method, triggering each
It That Betrays controlled by an opponent.
Resolve one of the It the Betrays triggers, causing an opponent to put
Bronze Bombshell from your graveyard onto the battlefield under their control.
Bronze Bombshell triggers, causing its controller to sacrifice it and dealing 7 damage to its controller.
Each
It That Betrays not controlled by
Bronze Bombshell's controller triggers, with your triggers being below each opponent's triggers.
Repeat from step 3.
Notes
The combo will work until there is exactly one opponent remaining. Depending on opposing life totals, this may or may not result in all opponents losing the game, or in one opponent surviving.