Pika's u-air spike?

[CanISmash]

this holds alot of pika's success... can anyone explain it. im not sure how to pull it off... there are times i think i have a feel for it with the spacing and distant but instead i just juggled the opponent straight up and other times they go flying back. is there a specific spot i should aim for when doing u-air? and if anyone wants to throw in any other pika tips while there at it go ahead. i use to main pikachu non-advanced techniques so i just wanna re-visit my old pal.

 

[Anther]

Mostly you just want to practice it a lot so you get a good feel for it.
The more you do it the clearer the picture of what you need to hit with to get the spike becomes. I could be more specific but I'm sure someone else'll come in and clean up XD.

 

[FrostByte]

Imagine Pikachu's tail as a clock (facing right). 6-10 would be lifting your opponent up, 10 to 2 would be the tailspike, (10 to 12 being reverse) and 2 to the end would be the back sending hitbox, from my experience.