Well, on "Five days of Flarg", Timmy's hug burned Mark Chang, and meanwhile, Fairyworld was burned down. And on "Fool's day out", Timmy was floating. And Timmy has been to Fairyworld plenty of times. Call this crazy, but I think TIMMY is a fairy.
I can explain most of that. If you've seen a certain episode, Mark Chang says everything on his planet was the opposite of earth, so that part makes sense because certain emotions like love can destroy him. The next one, I haven't seen yet, but I'm pretty sure that was an error or it'd have something to do with that episode where Timmy and his fairies switch places. And the reason Timmy's been to Fairy World so many times is because he wishes himself there.