Black Ooze (ブラックウーズ) is a recurring demon in the series, often as a palette swap of Slime.
In the Dungeons & Dragons fantasy role-playing game, an ooze is a type of creature. This category includes such monsters as slimes, jellies, deadly puddings, and similar mindless, amorphous blobs. They can be used by Dungeon Masters as enemies or allies of the player characters.
Many oozes dwell underground, and most secrete an acid from their skin that dissolves flesh and other materials rapidly.
Oozes are essentially blind, but more than make up for that with an ability called "blindsight", which allows them to discern nearby objects and creatures without needing to see them visually.