This is awesome! Haunted Mansion is one of my favorite DOS platformers, and this does a great job of updating the combat while keeping the original feel. It's very challenging and fun and the gore effects are hilarious. I can't wait to play the updates you are working on.
The biggest thing that I would like to see improved would be replacing some of the borrowed Dave sprites with original art. The basic zombie is the most noticeable one. This one in particular still feels like a placeholder, even though the new smoother animations look great.