Disclaimer: My Suggestions on how the NPC would interact with the player is a loose one that is open to discussion and interpretation. Some of my suggestions seem to be harsh but they are up for modification by anyone who thinks they have a more viable solution. Try to keep in mind I am only suggesting an NPC who is in spirit resembling Gary Oak, the goal of this NPC isn't to inconvenience the playerbase to the point of rage but to potentially inconvenience a player while giving them a fair opportunity to react to a challenge and if successful, gain back what was taken from them and more.
I think a factionless NPC who always feels one step ahead of you, becomes more powerful as you level, forces you into duels and on occasion interacts with you in an antagonizing fashion could really spice up the game. He would always pop up at unexpected times on a very random schedule, his appearance would be rare so that he isn't a complete pain in the ass.
-You're about to engage that rare mob? "Gary Oak" swoops down and tags it before you can and 1 shots him. (you would have the chance to engage Gary after the fact, if you win you get credit for killing the rare, the drops and a reward for defeating Gary)
-Engaging in open world PvP? "Gary Oak" swoops down and starts attacking everyone.(This would involve players putting aside their differences in order to defeat "Gary" or continue their conflict and both be defeated)
-You see "Gary Oak" swoop down and steal your Ore? You try to attack him but he just hops on his 6.0 exclusive flying mount and flies away /waving and /laughing at you because he knows you can't follow him. (If you hesitate he would fly away but you will have the chance to engage him in order to fight him for a dynamic quest reward and the ore/herbs he stole)
-You get sent on a quest to save a kidnapped citizen in order to gain a factions trust? You arrive at the kidnapping location to see a sign saying "Gary Oak was here" and he already completed your quest and took your reward.
-Out killing some mobs? "Gary Oak" swoops down and summons 6 monsters that he sends to attack you in gauntlet fashion.
-Doing some Pet Battles with all of your pets with low health? Goes without saying.
I think the potential for an NPC like this would be pretty awesome, he could be the self appointed "Hero of Draenor" on a mission to become the greatest and most versatile warrior that ever existed. Many people would look forward to putting him in his place at max level if he was made memorable enough through the questing experience. When you encounter him in duels he could change his spec/class in order to keep him random and interesting.
Of course he would be available to engage in some sort of Pet Battle tournament. Perhaps even swoop down and capture a rare pet you found and the only way to get the rare is to beat him in a duel immediately.
Let me know what you guys think, would you want a Gary Oak type character in WoD or WoW in general?
For those who don't understand Gary Oak's role in Pokemon this blurb if for you
I firmly believe Gary should be the rival in every Pokemon game. No, I don’t care if he’s 45 by the time Diamond and Pearl or whatever is out.
He should also continue to be a total dick like he was from day 1. He was 10 years old driving around a convertible and had bitches at his beck and call. This should continue.
Whenever you enter a cave and come out with all your Pokemon are at 3 hit points? Gary appears.
Get through Team Rocket HQ, out of any healing items with your best team reduced to rubble? Gary rolls up in his Mercedes.
When you finally attain all the badges you need, with your favorite Pokèmon battered and beaten? Yeah, Gary.
All your Pokèmon are knocked out and you’re 5 tiles away from the Pokemon Center -- Guess who just blocked the entrance way and says he challenges you to a fight?
Fuck yeah, Gary Oak