When charging upsmash, there are three hits: The actual Yoyo coming out, the part where it spins while charging, and the final hit when it arcs over his head. You have to do a charged Upsmash, but you only let it out for roughly as long as it takes Ness to blink yellow once, and only hit the character with the first hit. By doing this, the second hitbox (the part where it spins) drops and stays stationary at the target.
Then you can do a few things. You can interrupt a short-hopped Uair or Dair (or a PK Thunder 2 against the ledge) to attach that respective hitbox to Ness's body. That's a jacket.
You can also recall the hitbox by... you know what, just look up some videos, this approached TL;DR status for TFS members after the first paragraph.