Where did he get that mask come from? Same mask H4? That made me confused...
I think Halloween 5 beginning Michael escape and stumbles into a the nearly river, his mask wet and melt made face looks different. I guess
In movie storyline, the mask is out for a year, probably worn by the elements. We saw what happened to the mask in Rob Zombie's Halloween how it aged. For production purposes, fans hated 4's mask, so 5 wanted to improve it and please people. Plus, different guy under the mask, different shaped head. Director's choice, too, I suppose, wanted to go with a more menacing, darker, gothic look to go with the rest of the film.
"He came home." - Dr. Sam Loomis from the original HalloweeN
the bug-eyed mask of part 5 really pisses me off.
at least part 6 had it a little bit better..