The title is exactly what it says, this legendary beep noise from Fist of The North Star can play on the strike that sends people flying for not just Marth, but Lucina and Roy's final smashes as well.
Comes in two flavors:
The piercing beep noise only.
Ditto, but mixed in with the regular sound for when Finishing Touch lands.
I do have to warn that the sound may be a little loud by default, but if you really wanna be as memey as you can possibly be, there is a louder version.
In case you have a soundmod for Marth/Lucina/Roy's sound effects, a wav file for inserting it into an existing nus3bank is included with every version. Just replace the idsps ending with Final_03, and you'll be golden.