This is something a lot of players probably wouldn't even notice, however when doing the quest Vampire Slayer count draynor never deals any damage, even to a level 3 without boosted defence or gear.
The reason this is an issue for me is as a skiller I simply can't do enough damage before he despawns, i only get 24 hits with a scimitar or 16 with a battleaxe, even with super potions it doesn't seem possible without a lot of luck, so I thought I could rely on rings of recoil. Seeing as he does 0 damage every hit the ring never procs and he never takes recoil damage.
EDIT:
After now attempting priest in peril the ring of recoil did sometimes trigger from 0 damage hits from the dog so I'm not sure what's going on