Several years ago, I took a lot of runs at this, but I kept getting stopped by that ridiculous final boss, despite having all my lives on multiple occasions.

I can't say I had any different strategy this time, just did a lot of spin kicking, especially when that jerk turns invisible.

I've never learned how to do those knee strikes at will. Whenever one comes out, it's just like me playing Street Fighter II at the bowling alley as a kid, getting a hadouken to happen by accident.

This seems like the rare co-op game where 1 player mode is actually harder than 2 player. I think you get the same number of enemies regardless, other than that part where you fight your own shadow.