There are two main types of common enemies: Heartless and Nobodies.

The Heartless are shadows that take a persons heart for themselves. They are relatively easy to beat compared to the nobodies, and when killed, the heart is sent to Kingdom Hearts.

The Nobodies are those without a heart. They feel no emotion, but can feel physical pain. They are dramatically stronger than their shadowy counterparts, and when killed, nothing happens. They disappear into nothingness.