Malenia is arguably the toughest boss in Elden Ring, and a major part of her difficulty is that she can heal herself by hitting you with her sword attacks. There’s an issue with the game, however, that makes her even tougher — a bug means that when players summon an ally to help against her, she can self-heal without actively making contact with a player.
Let Me Solo Her, the premier expert on being summoned to fight Malenia, has posted a video of this bug from patch 1.04. Around the 8:30 timestamp in the video, you can see Let Me Solo Her fighting Malenia, and it’s quite a battle as she continually heals, even while Let Me Solo Her flawlessly dodges all of her attacks.
Let Me Solo Her is still able to kill her — after all, there’s a reason this player has become a legend in the Elden Ring community — but other players have noticed the bug as well. It’s possible that this comes from lag or a server discrepancy from online play; Elden Ring might have registered the attack hitting, but only partially. One player who goes by EX-Eva on Reddit had this theory:
I haven’t seen anyone post this happening in offline, which leads me to believe this is a result of the multiplayer stability improvements mentioned in the patch notes. As others have pointed out, you were likely hit in the hosts world but not on your screen, which would register a heal but not damage.
This lines up with how her healing works offline, when you die to her Waterfowl Dance, if she continues the attack after you’re dead you’ll notice her heal when she passes over your dead body even if she’s not dealing damage.
FromSoftware have been patching Elden Ring since the game’s launch; there have been numerous bug fixes in recent patches, including one that nerfed its extremely scary blood dogs.