I wanted to say decaying ftilt and fair are huge. fair links directly into ftilt,jabs, dash attck grabs etc. at lower percents and ftilt is going to be where you get most of you damage in the match up. try and tilt lock into a utilt since that will lead to direct follow ups similar to how an fthrow does which will allow you to continue your combos
bair combos like fair but since you want to use it at max range in the match up (the cross up "stomp" gets iffy against MKs who know how to use it. grounded shuttle loop can be used when you get in too close instead of even waiting for the sheild hit) I try to save it as a kill because of is range, speed, unique hit box (far behind and above sheik) and power (the SSbair)
http://www.youtube.com/watch?v=lFcmujjqUts
^
Me going over sheik's bair nair and fsmash hitboxes
bair combos like fair but since you want to use it at max range in the match up (the cross up "stomp" gets iffy against MKs who know how to use it. grounded shuttle loop can be used when you get in too close instead of even waiting for the sheild hit) I try to save it as a kill because of is range, speed, unique hit box (far behind and above sheik) and power (the SSbair)
http://www.youtube.com/watch?v=lFcmujjqUts
^
Me going over sheik's bair nair and fsmash hitboxes