Mental State, sometimes referred to as Sanity, is a variable very similar to .flow's Erosion Counter. The game registers certain events and interactions as an increase or decrease in a variable found inside the game's code.
The Mental State variable can be seen as Soutarou's mental health, which means the more you increase it the more he is depressed/unhappy. To avoid confusion, a higher Mental State can be thought of as a higher "insanity". Many events are only accessible with a low Mental State, and several negative events are more likely to happen with a high one, so you will have to be cautious if you want to see them all.
For your own convenience, it is recommended you have several save files for the game.
Increasing Mental State
Many events and actions increase your Mental State thanks to Mikan Muzou's dark nature.
The following is a list of ways to increase your variable. All of these except getting the Dark Hair effect are repeatable, meaning you can do them multiple times and they will continue to increase your mental state. You can repeat these events until you reach the variable's limit, 29.
- Waiting in Soutarou's real world room (random chance, can increase and decrease)
- Viewing the Hazy Memory event (+3)
- Toxic Sewer's Monster event (+2)
- Attempting to go upstairs while on the top floor of Prison (+1)
- Killing the pink blobs found in the Migraine Hallways (each does +1)
- Interacting with the strange device in Dark Sewers (+1)
- Getting the Black Hair effect (+3)
- Viewing the bad version of the God event (10% chance) in Sandy Sprout World (+3)
Decreasing Mental State
Decreasing your Mental State in Mikan Muzou is a bit more complex. Since you start at 0, it's usually easier to start a new save file to view events that are only accessible with a low Mental State instead of attempting to decrease it. Idling in Soutarou's real world room is inadvisable, as it increases Mental State more often than it decreases. These are also repeatable. You can enter the Sunset area, interact with its fence, leave, and repeat this process to continuously lower your variable.
- Interacting with the cat found in Archaic Temple (-1)
- Viewing the Sunset found in a door in Toxic Sewers (-2)
- Killing the shadow found in Prison (-2)
Checking Your Variable
The main way of checking your variable is by checking the position of the clock in Monochrome Pixel Room. To find this room, you must attack the Assembly Line chaser with the Knuckledusters with your bag off. He will teleport you to this area. The clock has four different positions, though notably the highest position is for fifteen and above; only half of the maximum Mental State variable.
Also in Assembly Line, the bottom right room has a large hole in the floor which will be replaced with a round red creature with an orange eye if you have a Mental State of ten or above. This can be useful for checking your Mental State without getting trapped in the Monochrome Pixel Room.
Events Affected by Mental State
With a low Mental State:
The Vending Machine Chaser is able to show up.
The NPC required for the Black Cat Flight event is more likely to show up.
With a high Mental State:
The Cave Chaser is more likely to show up behind Soutarou and eat him.
More hostile chasers appear in Red Hand Labyrinth. This happens with any variable above 7. A higher Mental State causes more to appear; this can make it nearly impossible to navigate without chaser-stopping effects.
The only event which requires a high Mental State is the Bloody Scenery event. While viewable with any Mental State, Soutarou will only fall to his knees and be woken up if is his Mental State is maxed out.