So in free for all, it's everyone against everyone (duh). Since everyone is technically an enemy to each other, how does Zenyatta's Orb of Discord work? Does it only enhance the damage he himself does on his discord target or does it enhance the damage of all players on the discord target?
Looking at the Zenyatta wiki on Gamepedia:
Coming directly from the Orb of Discord Official Description:
Attaching the orb of discord to an opponent amplifies the amount of damage they receive for as long as Zenyatta maintains line of sight.
Further down, under the Strategy / Weapons & Abilities section, you can find that:
When activated, Zenyatta will place an Orb of Discord on the targeted enemy, causing them to take greatly increased damage from all sources.
The specific phrase all sources indicates that any and all incoming damage on Zenyatta's Orb of Discord target would be amplified.
This does mean that whenever you use Orb of Discord, you are essentially helping your competition at the same time.