yeah, ike vs. mk isnt nice, one offstage dair from him and youve lost a stock, unless its high up of course.
im not really experienced enough to give MU's on everyone, but as for most higher tier characters, i can.
but, this is from my experience in a part of the world with a very different metagame.
i think for ike, against characters with gimmicks that ARE distracting and effect the game (grenades, bananas) its best to learn to use ike's DACIT effectively the amount of times i've caught diddy's off guarding by throwing a banana at him with DACIT and then gotten a free hit on them, (because literally, you slide right to where the banana lands if thrown forward) if they are at any sort of percentage, they will die agaisnt ike. thats diddy only of course, for snake. youre better off learning the sort of techniques a snake uses with them rather than jsut throwing them back or off stage.
and olimar...ugh what a pain. yeah, all i can say is ignore the pikmin, oliamr will try to hit you as youre trying to get them off you, if you ignore them and continue to focus solely on olimar, chances are they will resort of less effective tactics.
...
sorry if i went into too much detail there, but once again, UK metagame is different