Moonbeam or Moon Messengers are small beings of light that come from the moon and help The Man in the Moon protect the children at night with their comforting glow.
They speak in a silent language that only MiM and Nightlight seem to be able to understand and speak.
The moonbeams are nothing more than small beams of moonlight and their glow varies in strength, and are capable of banishing shadows.
One young moonbeam in particular, accidentally stumbled upon the resting place of Pitch Black, after he was defeated by Nightlight and fell to Earth. The Moonbeam was drawn to the diamond dagger embedded in the Nightmare King's chest and used its light to release Nightlight from his prison, accidentally awakening Pitch as well, and trapping itself inside the blade.
Despite its newfound imprisonment, the Moonbeam became fast friends to Nightlight and now fights alongside him against Pitch and his Fearlings. The moonbeam is very curious and while foolish at time, very brave.