Being released on the PICO-8 medium, the game can be played on various platforms. It was created by Jusiv and was published in 2017.
The player begins each game in The Station area. Here they must locate and activate several switches, along with finding a ticket. Once the ticket has been located and the player brings it to the boarding gate, it will open, they can then board a train and be transported to the next area.
The Open (the next area) seems to at first be an endlessly repeating area, although there are clues for the player to follow, which will create a teleport that will take them to the next area known as The Rift. Here the player's character must make it to the next teleport area at the end of the playfield, although there are several places where the player will be transported back to the beginning of the area. If they are able to make it to the teleport at the top of the area they will be transported to the next level.
In The Grove, the player must activate several areas in order to be transported to The Remains. Here the player must collect all blue blobs on the screen, which will open a door in a building at the top middle area of the level, which will end the game once they enter the building.
Three endings are possible, depending on what the player does during a game. If not all five newspapers are read and the player doesn't encounter the black creature all five times during a game (see Trivia), then the game will end with its statistics being displayed. If the player encounters the creature five times but doesn't read all of the newspapers, the creature will appear, asking the player if they thought they could just escape and the creature had "grand plans" for them. If the player is able to read all newspapers and interact with the creature five times, the latter will happen, but then the creature's speech is interrupted by someone telling it to leave the player alone. The player is then transported to a new room with an entity known as "the writer", telling them to ignore the creature and for them to leave, as they had gone off the script. However, their future was yet to be written.
- A newspaper can be found in every area of the game, giving clues in articles to the back story of the character's abusive parents and that domestic charges were filed against them. Their child had disappeared, which is the player's character.
- There is no mention of what sex the character is until the final newspaper is found, where the parents stated in the article that they wanted their daughter back. Once the full ending is viewed, the writer states the player's character's name is Jade.
- Jusiv, NULL's creator, created the previous game Messages, which was in regards to two unnamed teens texting each other over the course of an evening. After several texts are sent, several of them will first appear to state something very negative, then the message will change. The black creature's face will appear with these texts briefly before changing back to normal. Several endings of the game are possible, which at least one will show the creature just as it appears during two out of three endings on NULL, appearing in the player’s room.
- The black creature may only seem to appear during the final level of the game throughout an initial walkthrough, although there are ways to get it to appear in every level. It is not identified as to being possibly the main character's depression or self-doubt appearing as a physical entity. Jusiv had stated in the Pico-8 forums that what the creature actually is is open to peoples' interpretation.
- In Messages, Jade is mentioned as to being missing in a series of texts, making this game a pseudo-sequel. At one point during NULL the black creature tells Jade that her friends either moved on and or they moved away. One of the teens in Messages had just moved to California.
- Move--arrow keys
- Interact/cut short dialog--x, z or c keys
- Pause game/reset cart--enter or p key