Okay here's my review:
First of all, I'm happy that you want to make a boss in my build.Though after playing,I've found that it needs a lot of tweaking.
1.Because I already have a lot of events for my other bosses, I'm not sure how much lag would be created because of Clappy "moving". It may be fine though.
2.The "run away!" attack should give more warning to allow the player to run away. I've also found that it sometimes keeps sucking you in after he moves back to the normal position.
3.Some sort of events keep me from going in the "bot spawn" area(I suspect setRadiusImpulse), but I've found that I sometimes get pushed in that area, and I can't get out. I suggest using zone events instead.
OnPlayerEnterZone>Player>setVelocity>[enter velocity here]
This would allow the player to exit if he somehow got in. Instead of being stuck. I'd also suggest having this on the bot spawn.
OnPlayerTouch>Player>setVelocity>[enter velocity here]
This would be so if they got in and somehow stayed in, they would get pushed out.
4.Arent I suppost to die when I touch the lava?
EDIT:5. also, I think you should make it so you can see Clappy die.(you teleport pretty fast)
Once again, I am happy that you want to make a boss in my build. It usually takes me a while to "de-bug" my battles by the way. Also, any ideas for my "final boss"?