Henry Hatsworth in the Puzzling Adventure/WMG

In the cutscene when Hatsworth and Weaselby first meet, they clearly recognize each other; Henry mentions that Weaselby's dues to the Pompous Adventurer's Club are overdue. Clearly.

Lady D is Death.
None of her husbands left her by choice, and she's hanging around a graveyard...

The Master Piece just grants its wearer multiple powers, and presumably access to the Puzzle Realm as well.
Each piece of the Suit grants a different power; the Hat reduces the wearer's age, for example. With the possible exception of the Shoes, any one piece could open up the Puzzle Realm, including the Master Piece.

The age reversing effect of the hat was a failsafe made by its creator
Older, mature wearers have their vigor restored, but younger people who would be more likely to use the hat's power for immature ends are rendered infantile and powerless.