|Reside in||the Candy Kingdom and the Crystal Dimension|
|Known characters|| Lady Rainicorn|
Kim Kil Whan
|Introduced in||"Animated Short"|
|Latest appearance||"Jake the Dad"|
Little is known about the background of the Rainicorns, other than there was a Rainicorn-Dog War. One dog saved Bob during the war, so he and his family Ethel and Lady are friendly to dogs. Lady, Bob, Ethel, and Lady's children are the only known Rainicorns in Ooo. The three of them speak Korean, though not all rainicorns do.
Rainicorns are unicorn creatures with almost a full rainbow of colors down their body. They range in length; Ethel is about twice as long as Lady, who is in turn three times as long as Bob. Bob is roughly the length of a normal horse, though shorter in height. The only shown rainicorns are rainbow-unicorn hybrids. 
All rainicorns possess the ability to fly by intercepting beams of reflected sunlight and "dancing around on them." They also have the ability to change the color of any object by shooting it with a chromatic beam fired from their horns, and the power to stretch their bodies out to various lengths, much like Jake. They also age much faster than other creatures, as after a little more than two days Jake and Lady Rainicorn's children were already physically older than their father though due to them being rainicorn-dog hybrids, true rainicorns might age faster than two days.
- Charlie (Rainicorn-Dog Hybrid)
- Kim Kil Whan (Rainicorn-Dog Hybrid)
- Jake Jr. (Rainicorn-Dog Hybrid)
- T.V. (Rainicorn-Dog Hybrid)
- Viola (Rainicorn-Dog Hybrid)
- The term "Rainicorn" is a portmanteau of "rainbow" and "unicorn."
- Jake claimed that for thousands of years the rainicorns battled the dogs over territory in the Crystal Dimension. The outcome of the war is never outright stated, but it can be inferred that the Rainicorns have some stake in the dimension today as Lady Rainicorn's parents come from there in "Her Parents."
- Rainicorns may or may not eat humans, as in the episode "Her Parents," Ethel and Bob Rainicorn try to eat Finn. After Jake prevents this they settle for a picnic of "soy people," which is supposed to taste just like the real thing. Finn's reaction to tasting it implies that even humans like himself find it delicious. The implication that Rainicorns eat humans is a possible reason as to why there are no humans on Ooo apart from Finn.
- There is an alternate version of the Rainicorn-Dog Wars, the Monochromicorn-Cat Wars.
- Rainicorn is 무지개콘 (pronounced 'mu-ji-gae-kon') in Korean.
- Even though rainicorns are rainbow hybrids, they do not have the color orange on their bodies.
- However the Lady Rainicorn on the right has orange or a "dandelion" or "Jake" colored color on it.
- The episode "Jake the Dad" showed that Rainicorns age rapidly, as Lady and Jake's pups developed quickly from infants into young adults over the approximately two days when Jake was visiting, and once he returned to live in the tree-house with Finn shortly after this, he said that they were already effectively older than him.