The next car is probably a fart car, where everything is just a fart.
|—Sad-One and Glad-One bickering over what the next car will be.|
One-One is a companion of Tulip, trying to help her find a way back home. One-One can split into two halves, each with its own personality. The two halves are called Sad-One and Glad-One by the production staff, but as a single unit, they are called One-One.
One-One is a white robot with a black stripe that runs down the entire circumference of its spherical body. On the front, the black stripe has two white dots that appear to be Sad-One and Glad-One's eyes when they are fused. One-One has four retractable spider-like legs.
The body can easily separate into two identical and independent parts and can reattach itself together again. Each half is semi-spherical in shape with a black line at their base with a single white dot, their eye. The flat base of each half has four spider-like legs, similar in structure to when it was whole.
Not much is known about One-One other than that they have been on the train their entire life, as stated by Tulip, and that at some point met Tulip and joined her on her journey to get back home. It has also been revealed that Tulip first meets One-One as a snowman head, but anything else about this encounter is unknown.
As One-One is a single robot composed of two independent parts, it has two separate personalities. As a single unit, One-One often flickers between the two different personalities.
Sad-One, the sad half of One-One, is morbidly pessimistic, practically always having a monotone voice and acting very downcast no matter the situation. Sad-One is almost always in a state of despondency, often shooting down any hopeful remarks. Though Sad-One is always pessimistic, it will sometimes drop pearls of wisdom that, ironically, encourages people.
Glad-One, the glad half of One-One, is cloyingly optimistic. It has a strong sense of happiness, never speaking in a voice that is not overjoyed. Glad-One never deviates from his happiness and will always see life in the most optimistic way possible. Glad-One is also very naive, to the point of doing things with reckless abandon. Its naiveté, mixed with its strong sense of optimism, makes Glad-One have a strong lack of self-preservation.
- One-One's two personalities share similar traits with Wheatley from Portal and Marvin from The Hitchhiker's Guide to the Galaxy.
- According to Tulip, One-One has been on the infinite train its whole life.
- Sad-One is left-handed. This has correlation with many popular medieval beliefs that the left hand is the hand of deviance, sadness, and destruction. The right hand is seen as being the hand of happiness and prosperity, (hence the positivity with the word, "right," in the English language).
- One-One makes an appearance in the background of one of the shorts in Cartoon Network's miniseries Villainous.
- One-One's design was inspired by Star Wars, and other sci-fi robots.
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