While I'm thinking of modifiers to gameplay, how about a randomiser mode as well? In which all items dropped by enemies or gained through chests will be replaced by an item that could contain (almost) any item in the game. If I do this I'll probably add a secret interaction point at the start of the game which deactivates once you leave, meaning you can only pick the modifiers you want at the very beginning. Now I have to think of other potential fun modes to go alongside it though...

Well this idea changed a little. Before you leave the first room there's a special menu called 'Cheats', where you can type in specific commands to activate various effects. I haven't added the randomiser mode yet, but there's a cheat that gives you one hour to finish the game. If time runs out before you get to the final area then you automatically get the worst ending. There's another cheat that makes it impossible to lose battles but prevents you from unlocking any bonus content if used.

As soon as you leave the first room, this menu is disabled.