The Werehog was a transformation that Sonic took during the game Sonic Unleashed.
After Dr. Eggman had released Dark Gaia with his Chaos Energy Cannon, Sonic's body absorbed a part of Dark Gaia. This caused his hands and arms to grow bigger as well as grow claws, his shoes to have spikes, his teeth to get sharper, and his body to grow fur like spikes.
Fortunately, his personality didn't change and he was still himself in this form. Although he wasn't as fast as his regular hedgehog form, Sonic's strength had increased. Also, his limbs can expand and stretch out over certain distances, allowing him to perform different types of fighting techniques.
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