Marsdog, a bubbly quadru-ped, I have to admit, actually moved backwards. I reversed the video. So, there, it's out. I like Marsdog, it's one of the more harmless animated and physical creatures.
Hupfi III is a little less harmless. It tends to jump away to annoy neighbors or end up on empty parcels or stuck mid-air on the border to a no-object-entry land. But worst so far has been the arm counterpart to Walkies II - it had been peacefully twitching for over a day before I happened to be present to see it, suddenly and without apparent provocation, take off towards the sky. Not to be seen to this day, despite several region restarts, a support ticket, a live chat session with someone who claimed an object with the name given did not exist in the region. Um, t's stil taking up prims in the prim-count, thank you very much.