I do enjoy the Skeleton Keys, though, I do have a suggestion about them. Please listen well.
There should be Copper Skeleton Keys added, the Copper Keys that are slightly more common than Wooden Skeleton Keys & should be made for lower level bosses, especially those in Wizard City, but they can unlock Copper Skeleton Locks that uncovers more new Skeleton Key bosses & Skeleton Key Treasure Chest rooms in earlier worlds & maybe more.
Just a little something to provide for lower level Wizards, especially new ones, too. What do you think?