Dream Eater
Creatures that eat good and bad dreams.
Dream Eaters are creatures associated with sleep that feed on dreams. They come in two main types: Spirits and Nightmares. Every Variant has Spirit and Nightmare versions. Union χ reveals that many ancient keyblade wielders had their own dream eaters. They are central to Dream Drop Distance, where Sora and Riku encounter them in the Sleeping Worlds.
Spirits
Spirits eat bad dreams and help protect sleepers. They can become companions to Keyblade wielders, fighting alongside Sora and Riku. Many have colorful, animal-like forms, such as Meow Wow and Komory Bat.
Nightmares
Nightmares eat good dreams and plant bad ones. They are the main enemies within the Sleeping Worlds, where Heartless cannot normally enter. Many resemble Spirit species, but have different coloring and a distinct Nightmare emblem.
Chirithy
Chirithy are Dream Eaters created by the Master of Masters to guide and watch over Keyblade wielders. These Dream Eaters have the ability to talk. Each is connected to a particular wielder and can become a Nightmare if that wielder falls to darkness. Sora meets Ventus' Chirithy in the Final world in Kingdom Hearts III.
The Sleeping Dandelions
Union χ reveals that the Dandelions left in the data world enter sleep. Their Chirithy take on new Spirit forms to shelter their hearts, preserving them while they sleep. Its implied these are the Spirits that Sora and Riku interact with in Dream Drop Distance