Haven't seen one of these threads yet and there is no time like the present.
I'll start with the Belseraph arena. It appears to currently work something like 50% chance to kill the unit, if not gain 1-5 xp. Regardless get 1
for 3 turns.
I think it would be better with something like:
5% outright dead
5% lose 3 xp
20% lose 2 xp
20% lose 1 xp
20% gain 1 xp
15% gain 2 xp
10% gain 3 xp
5% gain 4 xp
Units that would end with negative experience die.
I'll start with the Belseraph arena. It appears to currently work something like 50% chance to kill the unit, if not gain 1-5 xp. Regardless get 1

I think it would be better with something like:
5% outright dead
5% lose 3 xp
20% lose 2 xp
20% lose 1 xp
20% gain 1 xp
15% gain 2 xp
10% gain 3 xp
5% gain 4 xp
Units that would end with negative experience die.