History of By Our Powers Combined…

A Mayhem (Crucible) medal triumph: "As a team, rapidly cast all of your Supers." The objective counts medals earned.

How to complete

1. Queue Mayhem (Clash or Rumble variants exist). Supers recharge roughly every 15-20 seconds, so a full team can have Supers ready together (Destinypedia).
2. Coordinate with your fireteam: wait until everyone's Super is ready and cast them close together.
3. Repeat until the medal count is met.

Notes

• A Bungie forum thread describes the medal differently, as one Super affecting an enemy while another finishes them (for example a Tether then a Nova Bomb). The triumph text says all teammates casting Supers rapidly; I could not confirm the exact timing window, so treat both as possibly relevant.
• In Rumble (free-for-all) there is no team, so play the team variant.