In N64 Perfect Dark my cousins and I (~10 years old) would set the AI team strength to max, make them aliens, and give them those little injection guns. It was the most horrifying/fun experience because they could move incredibly fast, were very short like Oddjob, and would one hit lethal inject you.
I once made the mistake of thinking it would be fun to choose the cow character model in a ‘Unreal Tournament’ tournament. The front of the thing is literally all head, so I was constantly headshotted :/
For me, it was the user uploaded models in Action Quake 2.
There were a couple that came to mind: a tiny gray alien with hitboxes to match as well as a model of Trinity (from the Matrix) that was all black and slimmer than the typical male characters.