To get the 90k of xp, all you have to do is get Waritu down to half health and then leave the arena. He stops fighting after you get to half health. Rinse and repeat for easy xp.
A friend of mine did it a few times... how they "fixed" this, is all you had to do before was talk to the guy to get the xp... now you just have to get him to half health and when he gives you the xp, leave and come back. Talk to him till he gives you xp then stop don't finish talking to him and leave the arena.
I found that just after you talk to him in the begining, run imediatly to the edge of the areana you can get some of the spiders cought on the bank which makes it easier to kill the rest. same with the other mobs in there