Damn my inability to remember the names of video games.

It was a 2D platformer.

It started out with the first level being a carnival, or an amusement park, I think. You could pick people up and move them around and stuff. I think one of the puzzles for the level was that you had to put the right amount of people on one side of a ride, or something.

I think the last boss of it was some sort of Lava or Volcano dude.

It was either on the N64 or the SNES, but I'm thinking N64. I remember that there was a race in one level, and a hint was that you had to double-tap the C buttons for a boost.