Strangely enough in TV and Comic cannon Nightcrawler and Wolverine are friends(maybe the best friends each of them has), and they respect each other a lot although they don't show it much(Didn't Wolverine call Nightcrawler 'Furball'? I don't know anymore, I'm a bit X-men rusty). So the cast shows it is even more genius, because that's exactly the relationship Radek and Rodney have.

Also Radek would use his disappearing powers for evil and steal Rodney's coffee and hang precariously from the ceiling making him jumpy.

I also like emo!John, he has a sort of self-destructive personality unless someone snaps him out of it. I don't think he's the cutting type, but the jumping without a parachute type? definitely.