I think that the thing in the vault in the tomb of the forgotten king is the wither from what i can gather breeze says its a "boss monster" and like its one of herobrines creation and herobrine the madman is the only one who would release a wither even for a war its a bit reckless and uncontrollable the only thing i cant figure out is it can only be subdued for som time obviously withers had been killed before or there wouldnt have been that beacon but i think im still getting somewhere