Alright, I managed to play a couple of Sheik vs. Lucario matches, and this is what I came up with:
*Sheik has been extremely nerfed since Melee, and they know it. Rub it in their faces, and 50% of the time, they will commit Hara-Kiri (Ritual Suicide).
*NEVER ExtremeSpeed horizontal to the edge when you are being edgeguarded. Always try to either recover below the edge or above it. Sheik users have a technique called “Vanish Edgeguard”, which is basically running off the edge and up-B’ing at the same time, which causes the explosion of their up-B to be lateral to the edge. This will usually KO Lucario at approximately 120% and up.
*Watch for Sheik’s f-tilt. They can trap you in it from 0%-30%. Also leads perfectly into u-tilt and/or f/n-air.
*You’ve really got nothing to worry about when you are directly below Sheik. All she has at her disposal is her d-air, when can be easily dodged, and her n-air, which is easily out-prioritized by Lucario‘s u-air. If she does manage to hit you with her d-air, no worries! It does minimal damage, and has an atrocious amount of landing lag.
*Sheik users feel awkward when they are above you. The only attack good Sheiks will use when they are above you is their needles and n-air, and since needle-canceling has been removed since Melee, needle-spamming Sheiks are much more punishable. If you can manage to pop Sheik into the air, you’ve pretty much gained control over the match.
*Up-Smash is one of their greatest attacks, and one of their main KO moves. A good Sheik will be able to Dash Cancel into Up-Smash, which can travel up to about half the distance of Final Destination. Fortunately, it is EXTREMELY difficult to pull off consistently. Still, be wary.
*F-Smash severely punishes bad DI. Try to DI up and out to avoid being hit by both attacks.
*N-air is the most common aerial kill move, and with good reason. Be careful when crowding a Sheik, as she will usually pull out an n-air.
*N-air, F-air, and B-air are lagless upon landing. WATCH OUT!
*Chain….*Snicker*
*Needles do not cancel projectiles as easily as they did in Melee. Take advantage of this, and spam them Aura Spheres.