Look at it! Look at it! LOOK AT IT!

Oh yeah, I got the model from Models-Resource.

Another lovely issue with that model was this gem (pun not intended).
ce19b2c.png
 
It might be a merged vertex or just two vertices in one spot painted to a weight. Unfortunately, it might be the former since Striker Luigi in Models Resource had the issue of an accidentally merged vertex in his mouth.
 
Yeah it was a merged vertex, which I'd already fixed. I was just giving another example of why this download was a mess. There were also no bones included. I had to add them all manually.