Puzzle in Dracula room:
Press the buttons on the mirror in Dracula’s room in the following order to solve the puzzle: 6 (lion),7 (girl below line), 10 (goat).
Inventory items:
Give inventory items to NPCs that you encounter to learn how they are used.
Cigarette lighter:
The cigarette lighter looks like an old nine-volt battery.
Keys:
Keys are not completely utilized until they disappear from your inventory. If one still appears, it still has a use at some point in the game.