The hunt solution: scaling HP (used in GW2 and WoW already...)

[Hyunckel]

I'm surprised FF isn't using this...

The premise is simple: when a hunt mob is being attacked by 10 players, it has enough HP for those players to kill it in 2 minutes.

When the same mob is being attacked by 100 players, it gains enough HP that it will take those players 2 minutes to kill it.

Final Fantasy 14 already uses a similar system with FATEs... If ten people go to a FATE the next time it will spawn it will have increased HP, even if you're solo.