I haven't unlocked this stage yet - I'm finding the Subspace Emissary a little... taxing.
I don't enjoy being FORCED to play as the crappy Ice Climbers and Metaknight especially (what a BRILLIANT choice of characters that was).
*cough* (SARCASM) *cough*
Playing through the SE generally the bosses can be tough or easy - when you're forced to embody say, Kirby, even Petey Pirahana can be a challenge.
At least when I unlock this mode I'll be able to take the bosses on with characters I'm familiar with.
So what your saying is, that you suck really really badly with Kirby?