Not really difficult.
Events should be every ( XXX mins)
Conditons should be none
Actions
All heroes will be moved to the arena except for the 2 duelist
The duelist will be chosen at random or the one with the most kills.
If one of the duelist dies, the game is resumed and everyone is back at their original position.
I'm not good with triggers, I can do it but I am terrible at writing them.