Dragon spear vs cockatrice just does zeros now because you need the mirror shield. But then it started getting hit by the spear's poison, lol.
I assume this is the same for basilisks and every other slayer monster you need the item for
I think poison is supposed to work even if you hit zeros, but obviously it shouldn't on slayer monsters that you can't attack.
Will be fixed with 2.1 :) added to the list