You never used Purrloin before? One of my favourite Gen 5 Pokémon, in fact. Not quite as fond of Liepard, unfortunately... anyway. Meet your new companion:
Take a Purrloin called Voldemort.
After supposedly being vanquished, Voldemort took flight and made his home in a new land. That land was Unova, full of magical creatures the likes of which Voldemort had never seen. He decided to possess the first creature he could, in order to investigate this new world further.
The creature he possessed turned out to be a Purrloin. Perhaps not his first choice, but the Dark typing was enough to persuade him to stay. He realises that his new body is weak, so he adds in his own Dark power - Voldemort may only use Dark type moves. A few other techniques will pique Voldemort's interest - he may also learn Slash, Toxic, Hidden Power, Hyper Beam, Shadow Ball, Shadow Claw, Dream Eater, Substitute, Rock Smash and Cut. He will also begrudgingly use Scratch until he can force the Purrloin to use something more powerful (most likely Pursuit at level 15).
Above all other goals, Voldemort strives to be the most powerful entity around, and will be furious if this is not the case. Voldemort must therefore be the highest level Pokémon on your team. If this is not the case, after each fight in which Voldemort is used, he will become enraged and banish one of your other Pokémon to the PC. The banish is in effect until Voldemort gains a level, or two levels if the banished Pokémon is Dark type.
When you reach the E4, Voldemort is enraged! Grimsley would dare to claim the title of Dark Master? You must fight Grimsley first. You only have one shot at this battle. What happens next varies depending on how the fight goes:
Voldemort the Purrloin
- May only use Dark moves, or moves from the following list: Scratch, Slash, Toxic, Hidden Power, Hyper Beam, Shadow Ball, Shadow Claw, Dream Eater, Substitute, Rock Smash, Cut.
- Must be the highest level Pokémon on your team. If this is ever not the case, after each fight in which Voldemort is used he will banish one of your other Pokémon to the PC until he gains a level, or two levels if the banished Pokémon is Dark type.
- You must fight Grimsley first out of all E4 members, and you only get one shot at this battle for the purposes of determining restrictions. Restrictions that follow vary depending on how many Pokémon Voldemort soloes throughout the fight.
Note that you don't have to send out Voldemort first during the Grimsley fight, so if you don't want to risk everything against the Scrafty he leads with, that might be a good idea. Up to you how much you want to go for. Oh, and for the record, if you have to fight Grimsley a second time for whatever reason, don't worry about soloing anything - the restriction is set from the first fight alone.
Hope you enjoy your new feline friend. <3
Edit: Ah, damn, Grimsley solo has already been taken. Give me a minute, I'll sort something out. :p