Difficulty: entirely in your hands
I want to call this “experimental”, but then, aren’t all of these experimental?
Something I’ve been thinking about a lot lately is games where the plot isn’t actually necessary. The world isn’t ending, your life isn’t in danger, it’s just a fairly standard story. And the game never explains why the protagonist needs to do it. It’s just taken for granted that the protagonist wants to go through the story, because that’s how games work.
(I can’t actually think of examples of this off the top of my head, now, but I know I’ve run into it.)
Of course, players tend not to notice this, because the entire point of playing a game is to do the thing that the game offers. So sometimes that’s the only reason the protagonist wants to do it: because the player wants to do it. Because it’s a game, and if you didn’t do it, there’d be no point.
Here is a completely trivial level. You can just immediately run to the goal. The point of Mario games is to reach the goal, right? There’s nothing stopping you here.
Or is the point to enjoy the experience of traversing a level? If you do that and enjoy yourself, even though none of it got you any closer to the goal, didn’t the level still serve its purpose?
Up to you!