Tried it out myself... and yes, it does lag a lot, lol. Well, on my end at least, it might be more a case of my client lagging, but I ended up getting 3 minute long chat lag when it got up to some of the higher waves... like 45+. Anyway, just to answer ya question shpp... it adds rewards to your inventory after you've left the arena, although I don't know how it works when your inventory is full.
If you want to see the arenas, you can do /ma arenas... or something similar, to show all the arena areas you can fight in, but either way, you can do /ma help to show any mob arena commands.
Last thing... I'm unsure if this is intentional, or whether it's just temporary... but in the default arena, no damage is on apart from when fighting blazes, wierdly. Might want to change that if possible so that there is full damage etc, since otherwise it may just end up with endless amounts of waves, as people just play for the easy, practically free rewards.
If you want to see the arenas, you can do /ma arenas... or something similar, to show all the arena areas you can fight in, but either way, you can do /ma help to show any mob arena commands.
Last thing... I'm unsure if this is intentional, or whether it's just temporary... but in the default arena, no damage is on apart from when fighting blazes, wierdly. Might want to change that if possible so that there is full damage etc, since otherwise it may just end up with endless amounts of waves, as people just play for the easy, practically free rewards.