Okay simple idea on this
In event tab you can click challenge to spar arena.
In this arena you gain 2x training speed. You can't rest, and can only challenge someone in a 10 level radius of you.
It takes into account your gs as well.
So if you have 500 gs you will train at 1k speed (500*2 = 1000).
Once someone runs out of hp the winner 1 gain 1 random stat.
You can only arena once ever 10 minutes.
The map should be a fairly small map so that the fighters can see each other easily, and get to fighting!