For gods sake, I can't decide what challenge to give you from my backlog...
DARNED INDECISIVENESS :P
OH, ok, time for some improvisation.
Take Indecisive the Nidoking!
As you know, Nidoking has a great, diverse movepool, and stats to match. Only problem is, he is very indecisive. very, VERY indecisive. As in, he won't know whether to keep the awesome moves he has learned, or to use other great moves, or to use them against that pokemon because it's super effective even though it would be weaker or switch to give someone else experience or.... ARGH SO MANY CHOICES. Hence, after you catch him, you have to raise his confidence in his choices. Therefore, here are your restrictions:
Moveset Restrictions.
Indecisive's moveset cannot have more than one move at 80BP or over.
His moveset must change by at least 2 moves after each gym.
Indecisive must have one attack in his movepool that is super effective against the upcoming gym.
If one of his attacks is super effective on an opponent, he can only use it every other turn.
If he cannot attack the opposing pokemon for super effective damage, he is under the effects of torment.
However, to raise his confidence in move selection, have him solo 2 Gym Leaders. After each solo, you are allowed to drop two of the above restrictions.
Also, to make a later restriction possible, he is not allowed to be taught move tutor moves.
Switching Restrictions.
He is not allowed to switch into a Pokemon if they have used a move that is super effective against him.
He cannot switch out to a Pokemon that the opponent is super effective against, or has a super effective move against.
If he is switched out, then he cannot switch back in for the rest of the battle.
When he is switched in, he must stay in for three turns before being allowed to switch back out.
If your opponents pokemon has a type disadvantage to one of your other pokemon and Indecisive is still your active pokemon, he must be switched out to the pokemon with the type advantage.
Again, to raise his confidence in switching, He must switch out, and let the next active pokemon take an NFE (to them) hit, 25 times. Then you can drop 2 of the switching restrictions.
And now, to make you a bit indecisive. There are 24 Moves in Nidoking's Movepool with a BP over 80 (Not counting breeding and Tutoring). You have 10 restrictions. If you don't like a restriction, you can choose to ignore it. However, you must RNG 2 numbers between 1 and 24. The two numbers called are the moves you are forbidden to learn. Think of it as buying out a restriction. If you call an already banned move, you must redo the random selection. There shall be no loophole abuse. If the banned moves make any other restriction impossible, tough luck, because you then must buy out that restriction too. That's what you get for trying to be decisive.
So, an Indecisive Nidoking, irritating restrictions, and a clause that makes it all better. Or all worse. What do you do?