Sonic, I have to disagree with your post completely.....ann I don't think i've disagreed with anything you've said in a very long time:
agree to disagree then.
a few things:
-Sheik's chain... I'm pretty sure MK's SideB and grounded UpB will beat it out even if it's being used perfectly, which it rarely, if ever, is. and he has enough range to get around it with a plethora of other moves if it's not perfect. especially from behind.
-Ftilt lock. I don't find it too useful against MK.... he just has to SH nair or dair out of it and ouch, you take more damage than he did. not that it isn't still okay, but it's not really reliable unless he doesn't know how to deal with it.
- Sheik's Uair. it's fast and has great power. it's not going to beat out MK's dair if he's sitting there waiting for it, but it's a great punisher if he's ever open.
-Sheik's Dair. I agree. a bad move... however. imagine you normally fall on MK with a nair from above, or something like that. because dair stalls, if MK reacts to sheik being above him under the assumption that she's going to nair and fall, the timing is going to be all off and it'll hit him. it's not an excellent move, but I hate how people just write it off because it isn't one of her go to moves. it has utility and, if you are finding yourself getting countered, it's a big change up that is normally unnexpected and, therefore, good for a surprise.
-Sheik's bair. it's good. it's always good. I just really don't see it behaving any differently vs. MK then it normally would and is, therefore, not worth much mention. keep in mind though, your leg, while the attacking part of you, is still a hurtbox.
-Sheik's Fsmash. Definitely her worst smash in the mathcup. but I see a lot of people avoid it like the plague. it's not that bad. it's horribly punishable, but it's got a lot more, for lack of a better word, "kick" than it's normally given credit for.
-Sheik's Dacus. Great against MK.... horribly punishable if you mess it up... which is easy to do with sheik's DACUS.
ZELDA
-Zelda's Usmash. I'm pretty sure it beats out anything MK has from above her. when he approaches from the side... well... it's just like a little marth heading at you with his fair.
-Nayru's. Ask anyone. I love nayru's. I am not a fan in this matchup. it has too little range and too much cooldown. against most characters, it's utility outweighs this, but often against MK the risk associated with using it seems to outweigh the potential benefits.
- Din's. MK is not really exceptionally fast as far as conveyance is concerned. sure, once he's close enough and not preoccupied it is punishable, as it always is. but at range and when MK is preoccupied, it's great. it counters tornado... that's just peachy.
-Zelda getting juggled. Lucky zelda has a really good airdodge. use it so that you're safe to land and then hope that he gets greedy. if he pursues you as you fall, he'll probably not be able to escape your reflexive USmash... which'll KO at pretty respectable damages. But really. zelda's not comfortable in the air. airdodge through him and uair if you can... that's nice. but don't try to take any of your lightning kicks against him in a dogfight.... it doesn't work....at all.
my personal opinion is that only Zelda/Sheik together can make this a close match if you're against an equally skilled MK, but that, if you don't understand one half of that duo, you're better off not using that half. MK can beat out Zelda OR sheik easily if they are not on their game.