Something I found that was a simple way of killing a Kab Kannon was to play as Riku. Go to TWTNW, and then go to the area "Fact within Fiction" - it's right after "Walk of Delusions". Then you'll want to go to where those purple lasers are that move back and fourth. You kind of have to push your Kab Kannon into them. Once you do that just wait and he'll die! Just do this over and over and you'll have a ton of Brilliant Fantasies!