You can cancel turn-around with whatever move so it would only cost 1 frame. However, if you are buffering it, like out of a d-throw, it doesn't cost any frames.
In the Ness MU i've found that you need to contest his landings and also be in the right position, below and in front of him, when he is in the air. Watch for dair in that position, but uair becomes your friend.
Ya, Uair beats it due to sheer speed. Well the most trouble Ive gotten is getting around his Fair for obvious reasons, though if he becomes predictable with the double jump Usmash and Nair are fast enough to intercept them..
T-Jolts against Ness is bad; D-Tilt (tip range) beats Ness' ground game; SH U-Air (back hit, tip range) beats all of Ness' aerials, except F-Air; Against Ness' F-Air: Shield-Grab (unless it's spaced,) boost pivot grab, SH-AD through it and behind Ness; Chu has a grab release chain on Ness; Offstage, hang on the ledge and wall Ness with U-Air; SDI out of PK Fire if it connects; Ness' will occasionally bait with PK Thunder aiming to hit with PK Thunder 2, hold that shield up and don't drop until it's 100% safe, then punish, or shield-grab (if Ness' PKT2 strikes the shield).
I mostly have learned to jolt at him offstage more then anything now. Didnt know the tip of the Uair beats his stuff, I assume that you would have to preemptively use uair though wouldnt you?
I know of the grab release chain, but is there any way of finishing it besides getting to the end of the stage?
Is it safe to follow Ness offstage and try to gimp him? I have difficulty doing so as well as preventing him from simply getting back on using Fair.
Lastly, I know you arent supposed to force the kill with Pika, but what should I be looking for when going for one? Ive had my friends Ness survive to ridiculous percents occasionally because I couldnt find any opening besides QAC Nair and I end up taking lots of gravy damage in the process.
Honestly Ive watched a few Pikas, including Esam, bait Ness to hop up with a fair and do a single jab, causing them to fall and potentially gimp themselves. Ive actually had this work a few times, but it is of course unreliable.