Shadow Doom (シャコーカサス, Shakōkasasu) is the fusion of Shadow and Samuel Nakaoka the Second's DNA code with the power of Crystal Stars; mixture with his created Kaucasus Memory. This form was first appearance after Shadow begin to conquer the Earth World and fused the Kaucasus Memory with the seven Crystal Stars.
With Samuel Nakaoka the Second finally gets the seven Crystal Stars, Shadow congratulates Samuel who got the seven Crystal Stars after The Three Endings. Samuel Nakaoka explains Shadow why he's congratulating him and he plans to become his ultimate form just like Melissa the Mitochondrial Eve.
Shadow Doom has the same powers of Shadow the Hedgehog's dark powers. However, his movement was combined with Kaucasus' powers and summon the darker colored-version of their minions. As the Crystal Stars was powered by Shadow, he enhances his attacks into more powerful version or recreates his own.
These attacks where Shadow enhanced:
- Dark Blast - His Chaos Blast's dark version. He shoot out on his mouth to tried to blast Samuel.
- Chaos Refresh (Hell Summon in Japanese) - Samuel Nakaoka's healing powers to summon/or revive the dark-colored version of their minions.
- Super Chaos Control - Shadow's upgraded form of his Chaos Control. He used his enhanced version of his Chaos Control.
Shadow Doom has only weakness is his consciousness.
- Shadow Doom's creepy voice was combination of Samuel and Kayako.