Heartless

The Heartless (ハートレス Hātoresu?) are beings of darkness that manifest in two forms, “Pureblood” and “Emblem”. While most Heartless are in fact manifested hearts, they behave entirely devoid of emotion, and thus were named “Heartless”.[1]
The Heartless are the primary enemy type in the Kingdom Hearts series, with various subspecies appearing as enemies in every game.
Nobodies

A Nobody (ノーバディ Nōbadi?) is the body and soul of a strong-willed individual who has lost their heart. While this enemy type makes its first appearance in Kingdom Hearts II, members of Organization XIII appeared in Kingdom Hearts Final Mix and Kingdom Hearts Chain of Memories, albeit as unclassified opponents.
The Nobody emblem is a splintered, upside-down heart that resembles Terra’s Mark as Xemnas remembers it.[1] It appears for the first time in Kingdom Hearts Chain of Memories, in which it is emblazoned on the Specter‘s head and designates sleightsused by the Riku Replica and members of Organization XIII.
Unversed

The Unversed (アンヴァース Anvāsu?)[1] are monsters that appear in Kingdom Hearts Birth by Sleep. They attack Terra, Ventus, and Aqua on many occasions over the course of their respective journeys.
Dream Eaters

Dream Eaters (ドリームイーター Dorīmu Ītā?) are creatures that debuted in Kingdom Hearts 3D: Dream Drop Distance. They reside in the Realm of Sleep and consume dreams, as their name implies.
There are two types of Dream Eaters: benevolent Spirits (スピリット Supiritto?), which feast upon bad dreams, and malevolent Nightmares (ナイトメア Naitomea?), which plant bad ones.[1] During their Mark of Mastery exam, Sora and Riku recruit Spirit Dream Eater to help them combat the Nightmares plaguing the Sleeping Worlds.