This gargantuan two-headed asteroid monster appears in Astromythos: Lair of the Spider Lord and Astromythos Book Two. He is one of the deadly cosmic minions of Lithozonas, a gas giant planet like Jupiter. His 5e-compatible stat block is found only in Lair of the Spider Lord, which is available here: https://www.astromythos.com/shop/pre-order-astromythos-lair-of-the-spider-lord