Alright I'll list that stuff here let's go.
1. Sheik yeah, she puts Pika in disadvantage.
2. Yoshi's annoying. Beatable though.
3. Doesn't every character lose to Diddy? I mean there's a chance Pikachu might have that MU even but...
(Bringing up customs because that thing is revelant) In some MUs Pika will want Thunder Wave to screw the other character. What characters are affected by TWave I don't know, possibly heavies and fast fallers. I would have to play with a Sheik, Diddy and Yoshi with customs on to try them out and it would have to be on 3DS.
Footstool combos must not be reliable