The really important thing to remember vs Sheik is that her aerial mobility is absolute tripe. If you find her trying to wall you with aerials, simply just walk away and F Tilt/Dash Attack her. Or wall her back with your Fair/Bair with the combined effort of Floating at about head height and your 2nd jump.
Bair is definitely my aerial of choice out Fair and Bair vs Shiek. I find Bair is very effective against an airborne Sheik because of it's speed and because most of the time it'll beat whatever aerial Sheik is throwing at you
Obviously if you're Floating all the time, Sheik will probably attempt a DAC Up Smash which is not good news if it hits. If you think it's coming, land from your Float with a Fair whilst moving backwards to wall it off.
Nair out of any F Tilt strings
Dair is pretty good at racking damage on her so throw in a few SH Dairs when the opportunity presents itself. Go for the Uair string if you're confident you can do it right
Edgeguarding is really important, watch how Kyon does it. Force Sheik into a position so that Sheik either dies or is put into a position where you can punish her
Kyon does a very good job of showing how Peach can tackle Sheik on the ground so be sure to watch those. If you're getting swatted a lot by Sheik's aerials then use more Bair and abuse the fact that her aerial mobility is very poor - she's certainly no Wario
Edit: lol crap, Buzzkillmatic beat me to it, I spent too long writing this
So I've been wondering - is there not a thread dedicated to LGBT on Smashboards? By no means do I have a problem with LGBT discussion here but I've always found it odd that there's no mention of a LGBT thread anywhere
