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The power level overall has gone up, meaning that there's a lot more stuff that can deal with these mons compared to before. Correspondigly, there's also more broken stuff that would be banned before them.
Rosenfeldius I think you're forgetting Aegislash - Ghosts can't be trapped by any means (I think?)
I like the idea of Snorlax blocking - if the whole Arena Trap flavour thing is really an issue for people, then it's a simple matter of making a clone ability with a different name (à la Huge...
Ditto's been fairly well covered by earlier suggestions IMHO.
I have two ideas for Mega Jolteon, both doing a fairly different job from what it normally does.
Mega Jolteon
Typing: Electric --> Electric
Abilities: Volt Absorb/Quick Feet --> Fur Coat
Stats: 65/65/60/110/95/130 -->...