Jareed
Jareeds were placeholders based on co-creator Jared Moldenhauer's head and used for multiple known and unknown levels, one of which includes The Light.
They can be programmed to move to any set path. If they touch the player(s), they will damage the player(s). In The Light's case, they move horizontally, from the right to the left, slowing down more as they get closer to the other side but then speeding up when they change directions. It is unknown how many debug levels this enemy is used in and was used in, but we know it is in at least three. It has also been shown in an early version of the branched path of the Sally Stageplay fight, where her husband dies. They are also the only antagonists in the test level DicePalaceTest.
Gallery
Jareed, as seen in (the now deleted) The Light miniboss battle, which was accessible from the debug menu but deleted in the 1.1.3 patch
Jareeds, as seen in an unused level, DicePalaceTest. Image taken from https://www.youtube.com/watch?v=G7I0VceHzRU
image taken from https://youtu.be/_LoNZdHnYCg?t=65