Thromnambular is a mystical wishing skull from The Grim Adventures of Billy & Mandy. In the series, he has the power to grant nine wishes, and upon the ninth is freed from his imprisonment within the skull. The wishes often go horribly awry. Thromnambular always speaks in rhyme. He is voiced by Dwight Shcultz.
In FusionFall, there are nine Thromnambular skulls scattered throughout the world, one for each wish. They are marked with a roman numeral from 1 to 9 (I to IX), and must be done in ascending order. Each skull has an associated hint mission given by another NPC, which must be completed before the skull's mission can be activated. Upon completion of the hint mission, the NPC will give the player a clue as to the whereabouts of the skull. The first eight skull missions are regular missions. The final skull grants a unique set of armor and a backpack accessory. Apparently, due to their remote locations and inability to fight or move, all 9 skulls were found and destroyed by the monsters in the future.
In The Fissure there is a Wishing Skull V covered in Fusion Matter. For the time, this one is not related with any mission. As there is another Wishing Skull V on Bravo Beach Thromnambular may be able to create and replace some of his skulls if they get destroyed.