To all having problem with beating any hellhound floor. Just re-spec into escape/willpower build, choose escape related trinkets and save after each encounter/key found. When hellhound catches you, Just run away. If IT fails, restart save and try again. You can save inside labirynth, so there is no problem at all. Run-collect keys-win-profit. No need to battle any of them. After you brute force your way out of labirynth, you can away go again and fight them to your hand-consent.
cheers and good luck. (Lamia is an impostor, ain't no way she's hellhound. Same Mother and father my ass)
PS:
Third floor is hardest, since you need to backtrack to find Keys that were shifted.
Last floor is easy, Just run in a circle and collect every key from tiny corners. There gona be a lot of battles, but again- Save game and run away every time.