Skull of the Corrupted Shaman at his sigil in a throne room arena. This is found in The Forgotten Ruins at a range of 350 tiles from The Core. Malugaz is an extremely tough boss who will probably still be a challenge while using equipment from the outer biomes. https://raymondagmqt.amoblog.com/um-imparcial-view-of-core-keeper-gameplay-51751706