Demon

Demons are supernatural and often malevolent beings prevalent in religion, occultism, literature, fiction, mythology and folklore.

The appearance of demons in the various TMNT universes has become a semi-recurring occurrence.

Mirage

 * Savanti Romero was once human, but was transformed into a demon by Lord Simultaneous as punishment for his crimes.
 * "Halls of Lost Legends" - Loki summons the demon Grendel to fight the Turtles.
 * "Raphael: Bad Moon Rising" features a demon named Lord Incubor, an inhabitant of the world of Nocturna.

Archie Comics

 * Null, a recurring adversary of the Turtles, is a demonic businessman who claims to be the Devil himself.

2003 Series
Tengu are depicted as demonic entities in the 2003 TV series.

2012 Series

 * Season 5 of the 2012 series introduces Kavaxas, the lord of the Demodragons, a race of demonic dragons.

Mirage

 * Grendel
 * Incubor
 * Savanti Romero

Archie Comics

 * Null
 * War

2003 series

 * Bone Demon
 * Oroku Saki
 * Shredder (Tengu)

2012 series

 * Demodragons
 * Kavaxas