Triple Threat Badge
From City of Heroes: Rebirth - Wiki
Description
While one Praetor is a challenge for the most potent of superpowers, you and your league masterfully tackled a group of three with startling simultaneity! You are henceforth known as a Triple Threat.
How to Get
Requires a VIP subscription.
Defeat all three Archvillains during the Battle Royale stage of the Magisterium Trial within 5 seconds of the first one's defeat, and then complete the trial.