The Glare was one of the three mobs that people are able to choose at the eleventh Minecon, or Minecon Live 2021. This mob would have had the ability to locate dark areas at the light level of zero, and became grumpy whenever it was shrouded in darkness. They could have been found underground as proven by the video, and they might have needed an opening to enter through.
This mob is the first mob out of three that you were able to choose during Minecon. The Glare lost after the first round.