Played from a first-person perspective, the game follows the five crew members of the freighter spaceship Tulpar after a mysterious crash leaves them stranded in space, trapped within as supplies dwindle.

The captain, alive but severely maimed and unable to speak or move, is blamed by the remaining crew for deliberately crashing the ship for reasons unknown.

When food and medical supplies begin to run low after two months, the crew decide to open their confidential shipment, but discover that it consists solely of mouthwash.

After failing to convince a drunken Swansea to let them into the utility bay, Jimmy and Daisuke serve him a tainted mocktail using the ship's sole bottle of rubbing alcohol.

After a series of visions where he is chased by a deformed mass of horse statues, Jimmy finds himself confronted by the Pony Express mascot Polle, who mocks him for his inability to take accountability for his faults.

[10] Art designer Johanna Kasurinen credits indie developer Puppet Combo for introducing her to the style, stating that "we don't need state-of-the-art graphics to make something impactful" in an interview with Rolling Stone.

"[12] Mouthwashing was first announced as part of a free update (inspired by Katamari Damacy) to developer Wrong Organ's debut title, How Fish Is Made.

The opening, which puts the player in control while the viewpoint character crashes the Tulpar, was praised by critics Bloody Disgusting and Rock Paper Shotgun for creating an immediate sense of tension and prompting curiosity about what has just happened.

[2][29] Writing for Paste, Elijah Gonzalez felt that the game's nonlinear narrative enhanced the sense of intrigue by driving speculation on preceding events.

[30] Keith Stuart of The Guardian praised the game's visual style for its ability to generate unease in the player, comparing it to the work of surrealist filmmakers David Lynch and Dario Argento.

[27] Writing for Hardcore Gamer, Kyle LeClair likened the graphics to fifth generation video game consoles, arguing that they complement the Tulpar's retro style.

[25] This comparison to fifth generation titles, particularly those of the original PlayStation, was echoed by Harold Goldberg of The New York Times, Ronny Barrier of IGN, Azario Lopez of Noisy Pixel, and Oisin Kuhnke of VG247.

[24] Ed Thorn of Rock Paper Shotgun called the Tulpar a "brilliantly realised space", citing the game's use of twisting, narrow corridors, but argued that certain scenes tended towards "surrealist tunnel meandering".

Kyle LeClair of Hardcore Gamer felt the characters had "nice and colorful personalities", and Katy Hanson of Rely on Horror found them "charming and memorable".

[1][25] Writing for PC Gamer, Ted Litchfield considered the horror to be built upon human drama, featuring themes of "failed ambitions, resentments, and regrets of people forced to work a dead-end job".

[25] Aaron Boehm, writing for Bloody Disgusting, argued to the contrary, claiming that the gameplay "always complements the narrative and mood of the game in a way that justifies it being an interactive piece of media".