Except...
[spoiler]Everybody knew Qilby was a dick, ever since he appeared. Mostly thanks to an Xbawx Live Arcade game Islands of Wakfu (which is also available in english). Which established and explained many things. I don't remember everything exactly, but Qilby had problems with everything and everyone all the time.
Also, he changed his personality? REALLY? Sure, up until now, he was calm. But did you even stopped to consider that maybe, just maybe... he hasn't changed all that much? In fact, even though he's now laughing more and is acting kinda crazy, he still retains his old attitude. Esepcially when he went to Rushu's world. He wasn't really laughing there, or acting too crazy.
Besides, look at it this way. He merged with goddamn Eliacube, he got his arm back (which WAS ecstatic for him, especially when he punched Grougal in the face.), and as he himself said, he remembers every one of his past lives, unlike other Eliatropes.
It's obvious the guy is quite crazy, if only because of the remembering past lives thing.
Moving on.
I myself, believe that Qilby at first really wanted to just simply get his people back, but after the meeting with the representatives of all 12 races, which ended with Prince of Brakmar starting a "WE WANT DA ELIACUBE GIMMEGIMMEGIMME" thing, Qilby probably said "[tornado fang] THIS" and decided to just drain the World of 12 of its Wakfu and then move on.
Speaking of which... you probably don't know, but Qilby was never the king of Eliatropes. It was Yugo. We knew that too thanks to the Island of Wakfu game, back when episode 6 first aired.
This guy was from the beginning setup to be a villain.
Nox himself, as much as I like him, wasn't that interesting until episode 13, his fight with Grougal and the last few episodes (including the special).
We stil have five episodes to go, including a four part finale. We'll probably see him explain himself in greater detail later on, and maybe even redeem himself.[/spoiler]