No es que tenga invencibilidad, es que falco se teletransporta varias veces durante este movimiento en espacios relativamente pequeños, como zelda, que no la puedes dañar una vez desaparece hasta que no vuelve a aparecer.
Edit: no, la he liado parda, eso me pasa por leer entrelineas, simplemente leer el quote.
Sacado de falco boards:
Phantasm Mechanics
Phantasm is a unique move that few people know the mechanics of apart from the basics. This bit will explain a bit more how phantasm works down to frames, hitbox and hurtbox levels. It's not mandatory to know how this works, but it can help with decision making.
0----------1----------2
Use the image above as a model for the phantasm.
At point 0, Falco is in the start-up lag of the attack. Once the start-up lag is finished Falco will appear for a single frame at point 1. On the exact frame Falco appears at point 1, a hit box appears behind Falco, but Falco himself at point 1 is nothing more than a hurtbox. That means that any hitbox that appears at this point will hit Falco out of the phantasm. On the very next frame Falco from which Falco appeared at point 1, he will appear at point 2. Another hitbox appears in that length between point 1 and point 2 on the frame falco arrives at point 2. After that frame, the hitboxes disappear and Falco is in the ending lag of the attack.
This information my seems pointless, but is in fact very useful. It tells us that phantasm can be unpunishable when spaced correctly. If someone is charging a move to hit Falco out of the phantasm you can adujst your postition slightly to place the hitbox of said attack between the points where Falco cannot be hit (which is between points 0 & 1 and points 1 & 2).
