Needles to lock a sword down

[Journal]

https://www.youtube.com/watch?v=w5fEartc-v8 (12:00)

So around here, Shroomed does something super interesting. When Marth does a forward aerial, he throws a needle at it and that makes Marth lag in stun for a second, and then Shroomed follows it up. Is this the sort of thing that can be done on reaction, or is it something you have to call out? Is it particularly useful?

 

[Scroll]

So what happened was Shroomed threw a needle storm at PPU at 11:57.
Throws another needle which gets shielded.
Shroomed goes to the Ledge.
Comes back on with a ledge hop needle.
Then comes what I think you're talking about, which was simply a Power Shield, Shield Grab on PPU's Fsmash.
The commentators called "Needle! Lag!" but all it was was a PS.
A standing needle has a bunch of lag. I am not sure what you're asking

EDIT: woah I am a dumb***. I see what you're saying. So the Ledge Hop Needle lands on the ground and made PPU enter hitlag as he hit it's hurtbox. In this case I don't see the big difference it made though.
It's uses has been discussed briefly before. Sounds like some obscure tactics if you ask me - but good to know of the physics regardless

 

[EddyBearr]

Darkatma uses this a lot. It's pretty good, and can throw off L-cancels.