No, it's not a speical pet. Even though you can get a Greater Imp pet from Grubb and a boss on halloween which gives an Imp item card, the regular Imp pet with no card is a pet you can buy from the WC pet shop.
Why it's no auction and all the other none card giving pets can be auctioned off is beyond me.
Maybe a mistake on KI's end or something, I don't know.
