lagless land that's interesting
I can do no impact lands onto the platforms with marth (if you do a hax dash/wavedash off the edge and jump forward instead falling to the ledge) but there's no attacks involved
this is so trippy I wonder why this is even a thing and if there's more of it
AIs(Aerial interrupts) are actually fairly different than NILs. both are consequences of ECBs(environment collision boxes), which you can see in debug mode.
normally in melee, characters land on their knees. the "landing lag" of just landing normally is the animation of them going from "on their knees landing" --> standing. in a NIL, you "land" in a way that your feet are in positions where the game thinks you are already standing. NILs have 1 frame of lag (WAIT0) that is unavoidable. the next frame could be an attack.
in an AI, an aerial cause you to shift your ECB downwards, such that you trigger a collision with the floor (whereas if you didnt do the aerial, you would be too high above the floor to land). this causes you to land on what would be the first frame of the aerial, which on a lot of aerials is during the window to autocancel it (4 frames of lag with most characters).
from playing around, i also found AIs with pika and marth. there are definitely a ton more in the game! kadano has a chart with grounded actionable intangibility stats, it shows which chars we've found AIs with so far.
all these effects are more easily understood with ECBs on.
also those are pretty rough explanations, you should look at Kadano threads for more rigorous explanations