1) Use the search function, Pets have been suggested more times, and in more forms than I can count in the past. It'll save you the trouble of getting flamed next time :/

2) Because I'm too lazy to repost all the reasons pets = NO, here's a link to a wall of text that explains it (not all points apply to your suggestion, but most do):
http://forums.spiralknights.com/en/node/50907#comment-346385

3) Now please graveyard this before pure hatred enters. :x