After you killed the black knight in the hallway at about 6:15 did you go back to your starting cell and grab the item there? It doesn't look like much but holds a big secret. Another fun thing in the Undead Asylum is Snuggly. In the outside area where the giant crow drops you off there is another smaller nest over on the side. It's easy to miss but worth investigating. Also, you gain no damage from raising strength or dex because you made your zweihander into a lightning version. That gives you some nice elemental damage but it killed your scaling. You won't be able to raise your damage through leveling up too much but you already have enough damage to beat the game how you got yourself set up already. I can't remember if you got your sword up to a +5 but that would be the main way to bump your damage up more.
Man hit ultra instinct this ep. Hitting parries like nothing and wiping out four kings like its nothing. the stray demon is meant to be fought before the fire version you already beat.