I've got to go with the only Elementals and Oozes make sense. Generally big magical robots have some weak spot (just look at Talos from Greek myth and his Achilles' heel... except he was killed by a group that included Achilles' dad). Undead rely on structural integrity, and vampires can be head shot just as well as anything else (if any undead are questionable it is the incorporeal forms and maybe liches).