Level progression will follow a mostly linear path. Well, I say linear, but it's more of a wiggly line that sort of wraps around in a spiral shape, but linear as in there is one main route to follow.
The very first few levels will be Surface Thoughts. The usual things that are on people's minds, and slowly the levels will proceed deeper and deeper down the spiral until they reach Internal Thoughts, followed by the Innermost Feelings, and finally the Subconscious. The levels will get progressively messier, grimier and more chaotic, because I love the pun of "spiralling into madness" and how the person's mental health is slowly worsening. I want it to feel bleak and the Subconscious will be the most conflicted portion of the person's psyche.
The last level of the Subconscious is the Subliminal, which requires one to break the level (literally) to enter the sensory perception threshold, the Limen, also known as the Liminal Point. It is the place where an emotion must be elicited in the person through force, but must be done so with care, for anything beyond a certain point can either send the person into shock or induce hallucinations. The person must be given feelings that make them feel better and heal them. If done carefully and successfully, you get the good ending where the person recovers and the madness in their mind is slowly phased out. If done wrong, the person's psyche deteriorates to the point of no return, and they break. This is the bad ending.
Enemies will be based off of intrusive thoughts, impulses and nightmares.
Although the plot is linear, I hope that eventually I'll be able to add side rooms where you can experience Memories or Dreams, things that the person remembers or witnesses at night. The Memories will be places which need repairing, because the person is starting to forget the good things in life and can only remember memories which cause pain. One of the bosses in a Memory will be Guilt, another will be Regret.
Dreams have slightly more surreal things happening, but will be plagued with Nightmares, which are demons of various kinds (also surreal and horror based). I know for sure I want to make one of the bosses Insomnia, and another boss be Falling, and a third that is Restlessness.
The game will a platformer-like dungeon crawler with a few puzzle elements. All items are rare - you make do with whatever you have and some creativity. There are no consumables - if you lose health, you have to be creative :3
I haven't thought about a tutorial just yet, but I don't plan on making the gameplay all that difficult (it'll mostly just be movement and like a few buttons at most). So the tutorial would likely just be a few pop up messages in the first level that you could disable in the settings.
It will take all the hugs that I can give and probably several more to take over the world, but hugs will definitely heal the entropy inside the person's brain.
Thank you for your questions Charlie! It was pretty good for the brainstorming haha