Artifact figurine, the gimmick of which is that it will always turn into a pet if not cursed, and the monster it turns into will fight anything without fear and maybe also has some extra buffs. When it dies, it reverts to the figurine, which immediately has its artifact cooldown set and can’t be applied again before the cooldown ends.

The inspiration for this idea was the Guenhwyvar panther figurine from the Legend of Drizzt, so possibly this artifact could just be named Guenhwyvar and be a figurine of a panther, which already exists in NetHack.