The Minecraft spirit

It gives you a Halloween armor set when you defeat it it can go through blocks when not transformed but first it watches for a couple days and you get a book to know about it, and it has minions and can transform into spooky stuff and his final form is the Grim Reaper and you also get weapons when you defeated it called the grim set and it has to transform for you to hit it, and it has a biome called the spiritual dimension