Forces Beyond is a stacked gear perk on the Transcending Helm. It greatly extends breath-holding while swimming and gives much stronger resistance to explosions, poison and fire.
You can stay underwater much longer, and explosions, poison and fire all hurt you a lot less. That covers most of the heavy damage in big fights.
Wear the Transcending Helm on your head slot.
Yes, it is one of the strongest head perks for loud play. You give up stealth head perks like Disguise to use it.