Uhm, well, the matchups aren't really all that hard for me, but there are a couple characters with a few annoying moves though.
MK's neutral b. Haven't met a character that uses MK yet, but I've seen vids that abuse this move, devastating Olimar's game.
Pit's neutral b. OMG. My friend aims really well with Pit's arrows.
Wolf's forward b and f smash. Well I guess it's my fault for jumping a lot when I need to chuck Pikmin, and my friend gets me with a forward b, although it has yet to kill me. And yes, very much dislike the outranging of the f smash. Wolf's hard to approach for me.
ROB. Those aerials confuse me, because well timed, it seems like it overprioritizes nearly all of Olimar's aerials, plus his neutral b and side b can really catch you off guard.
Another Olimar... I mean, wtf. It becomes a forward b game, and both sides have the ability to shake off pikmin with nair, unless one person has a whole bunch of purples he can abuse to approach safely. On the other hand, the opponent might have that advantage too...
These matchups don't hinder me from 2-3 stocking my opponents anyway (except for the Olimar, which is the toughest battle for me), but I guess these moves can be used against me at better tournaments and such. Not cool.