Good fiction doesn't counter-act bad game design. What the players experience will be what is, not what is written.
If you'd wanted to design for a Pet v Pet battle, a basically Despise Pokemon, you should have set it up so BOTH armies are untouchable except to the karma AI spawn until a final battle, where the two brothers lead an armies in an arena; I'll explain why shortly. Have the pets nice and strong, so as to be genuinely useful, but attackable in the final battle. And have the two brothers spawn at once and lead the fight, the strongest army will tend to win and kill the other. One could start on Ogre Isle and one at the entrance, if you fancied having them "march" to meet each other for atmosphere. At the point of victory, both armies roll individually for artefacts as currently, taking damage into account to encourage further army training and PvM in that battle, but the winning side also gets a nice extra Heart bonus (from "The last breath" of the brother if both are now face down) to spend outside at the wisp. Argue that the loser shouldn't get anything? Congratulations, you've just ensured that negative karma players are excluded from the dungeon entirely, as they will be a minority on every shard, so why risk losing out? Get a positive karma character and farm the mechanic instead. For both sides to want to play, both of them have to believe at least they can win in some way by doing so.
This took me literally a minute to think up, and already is a better idea than we currently have because it takes into account something programmers are often incredibly blind too; actual human nature, which is corrupt, selfish and self destructive, or just plain not able to flourish within cold, logical rules as laid down by a computer game and the sensible minds that often design them. You need philosophers not just programmers to design events though.
I mentioned I'd come back to the question of why player pets shouldn't be able to fight each other later... because right now, do you want proof of just how slow witted the "l33t PK gri3f" types are? Whilst bragging they know how to kill people better than anyone else, I notice none of them have worked out over the entire weekend the simplest way to completely break any Despise variant that allows pets to be fought... cast poison field on the entrance gates themselves (and, if it's possible to move pets manually down the stairs, on the stairs between the two levels to get players passing both ways). Pets passing through will have to pass through poison fields, will flag and stay flagged the instant they try and cross the levels, it can't be avoided, the pets will all be low level and there won't be time to prepare to defend it. The only way to play then will be to force people to stay on the same level and use the karma swapping trick to go to L15. And of course, as the griefers are all such smart bad boys with negative karma, you know what floor everyone else will thus likely be on. 2-3 people can thus destroy the entire dungeon for everyone, 2 on the gates, and one upstairs locating people's positive karma, or now negative karma training on the positive pets there, all of which are valid targets. For added annoyance, you could probably kill all the AI as well so they couldn't even tame one...
DESPISE IS ATROCIOUSLY DESIGNED. IF IT WEREN'T, THE HALF WITS WOULDN'T BE ABLE TO ABUSE IT SO.
So instead of Despise I spent my in game time over the weekend happily swapping my store of harpsichords and sands for those who needed specific numbers, whilst idly farming rolls for my own instead... so much more productive and beneficial for the souls of all concerned.