I was looking at this game on steam (Ninja Reflex)
My 7 year old brother said "Look it a Cube from the portal video, hax"
I was like "no it isn't" but then I looked again and was like "Dude!"
300 Ninja challenges to conquer.
Go from White Belt to Black Belt, 3rd Degree.
50+ Steam...
Ok tell me...
What the skin is for (Alyx skin, zombie skin ect)
&
What folders are in the ZIP/RAR.
Then I will have a better chance of helping you.
I doubt it's a model as it worked in HL2 unless it was a well done model with it's own animations,That I doubt.
I assume you put the skin in C:\Program Files\Steam\steamapps\username\half-life 2\hl2\materials
Just put it in C:\Program Files\Steam\steamapps\SourceMods\gmod9\materials instead.