What defines 2P for a run? Is it spawning Gooey, using Gooey, or having a second person control Gooey? In my runs I use Gooey, but I control him myself.

2P is taking control of Gooey. Just spawning Gooey would not make it a 2P run, since it can be done on the first controller.

I'll clarify that in the rules.