So I landed a Roy dair spike....

[hi im dennis]

Ye uhhh, I wasn't even aware that this was a possible....... Someone please explain this phenomenon.

 

[G13_Flux]

i think the easiest explanation is that if you spiked someone with his dair, his dair obviously has a spike hitbox somewhere. no explanation needed really, just investigate the game yourself.

this is a very known thing. the PMDT even has it stated on their character description of him on their homepage. its not a phenomenon, just.. design.

 

[Sundark]

There are two very small hitboxes located on Roy/Roy's arm when he uses Dair that cause a fiery spike (as of 3.5) to occur, however if you connect at all with the sword hitboxes during the move, they take priority and you will "sweetspot" instead for a pop-up. Comboing into this hit is possible using Fairs, Dtilts, and even other Dairs. A good way to practice it is to aim such that you hit them with Roy's armpit, or his head, as you are jumping into your opponent. I find it especially effective on Samus, especially on tether getups. Big characters such as Dedede can be trickier to hit with it since they are more likely to get hit with the blade if you don't start it a little earlier.