Nightcrawler

The Nightcrawler is a beast with a wispy dark appearance and blue eyes.

The Nightcrawler has a layer in the swamp right above a deep dark city. The nightcrawler dwells near a mangrove tree, which corrupts its surroundings and comes out at full moons hovering around it. It won't be able to get to far away from the corrupted tree. The Nightcrawler will also be able to dissipate into wisps of shadow, rendering it invincible and invisible but also unable to damage. When you are near it, it can drain you of your health with withering and can give you the darkness effect.

On death it drops special items that can be used to create magic items, such as:

Wisps of death, eyes of shadow, scull of night, which can be used for banner designs, and can be combined with each other and some other materials (i.e. netherite, diamond, iron) to create armor sets and weapons. The scull could be used to create the staff of nighttime, giving off the darkness affect and withering to nearby players and mobs. The eyes of shadow can be used to increase the light level for the player using them and can bypass any darkness effect.