SHEIK:
Sheik will **** YOU UP. don't expect to win against any Sheik that knows how to combo you. I'm serious. Go read the MIOM Marth/Sheik guide (it's on my guide list on this board) first. Know grab followups on her, (fthrow, ftrhow, uthrow, utilt) and be able to move well around her on the stage. Learn to DI her downthrow, and ftilt. Good edgeaurds pls (a good one is to let her land onstage with her recovery, and use the lag to ledgedash and then reverse upB.)
I don't know much about IC's yet.
SAMUS:
WavedashOos for them missiles. Learn to powershield (another thing I forget to mention, learn those two for Falco as well). You can get really good juggles at low % from her weight. If she is recovering high, edgegaurds are pretty easy (just watch when she uses downB) and if recovering low with tether, try and steal the ledge first and then punish.
Are these helpful at all?