Arena? What is the Arena?

[thejeff]

Actually if you win and have a hand slot (Two? The Trident is two-handed, right?), you get the prize.
It is cursed so the Champion has to keep it and when another death match happens, the Champion will automatically attend.
(Unless that's changed since Dom2. I don't think it has.)

The Champion is assumed to be the current holder of the trident, so I'd assume it's possible he could be killed and someone else pick it up on the battlefield.

In Dom2, the AI would often send their god in. I haven't seen that yet in Dom3.