Void Monster/Prawler

When below bedrock in the over world or above bedrock in the nether this mob would spawn. It would act like a vex but move faster and more random. It wouldn't phase through bedrock of course, and would be immune to all damage except for wither and would blind everyone nearby when killed and drop an item with more than 1 use. It would look similar to haunter from Pokemon. They could also drag you maybe so if your ice boating it could try to pull you out the boat with a funny animation. Maybe an infested totem, up to Mojang since they usually have good ideas.