In the video game Sonic Unleashed, the Werehog is a lycanthropic transformation of Sonic the Hedgehog. After being exposed to the negative energies of Dark Gaia, Sonic would be doomed to change into this monstrous shape whenever the sun set. While this form may look ferocious, Sonic still retains his normal personality; he is daring, adventurous and a little cocky, but has a strong heart and hates injustice. However, Sonic loses his trademark super-speed and agility when he turns into the Werehog, but makes up for it by gaining tremendous brute strength and savage fighting skills.
After supposedly thwarting his arch-enemy Dr. Eggman once again, Sonic found himself suddenly caught in a diabolical trap. The doctor used an energy-siphoning system to drain Sonic of the Chaos Emerald energy he had harnessed for his Super Sonic form and sapped the emeralds of their power, transferring it to an orbital weapon called the Dark Chaos Cannon. The satellite weapon fired a beam that shattered the planet into fragments, yet the broken continents remained in close proximity to the planet's core and each other. Eggman's intention was to awaken the demonic creature at the centre of the planet called Dark Gaia so that he could harness its energy in order to build Eggmanland, a hi-tech megalopolis that would be the capital of the doctor's global empire.
The Dark Chaos siphoning system had an unexpected affect on Sonic, turning him into a bestial form that Eggman called "festive". Eggman then jettisoned Sonic and the Chaos Emeralds from his satellite, letting them fall back to the fractured planet below. Sonic survived his crash-landing and soon after met a peculiar creature whom had lost his memory, a creature that Sonic would name "Chip". Feeling responsible for Chip's amnesia (He had landed on him, after all), Sonic decided to help him try and recover his lost memory while at the same time figure out how to repair the damage Dr. Eggman had done to the planet.
As Sonic and Chip travelled the world together, Sonic would come to understand how his Werehog form worked and how he could best put it to use. While he lost his speed when he transformed, he became incredibly strong and used this awesome power to ferociously pummel the spawn of Dark Gaia that had been appearing around the world, as well as destroying Dr. Eggman's Badniks wherever he found them. With help from his friend Tails and the scientist Professor Pickle, Sonic and Chip learned that the world could be put back together by taking the Chaos Emeralds to the Temples of Gaia, seven ancient structures located on different continents. With the emeralds placed inside the temples, their energy would be restored and rebuild a balance between light and darkness.
Sonic and Chip's journey would eventually take them to Eggmanland, Dr. Eggman's new city, which had been built on top of the last Temple of Gaia. Fighting his way through Eggman's forces, Sonic reached the temple and restored the final Chaos Emerald. However, Dr. Eggman had also succeeded in restoring Dark Gaia and Sonic was forced to fight the beast before the planet could be fully repaired. Dark Gaia became whole after absorbing the dark energy that had afflicted Sonic, which allowed Sonic to return to normal. Using the Chaos Emeralds to go Super, Sonic defeated Dark Gaia and restored the world to normal, though Chip would disappear afterwards.
Sonic is normally capable of pulling off remarkable acrobatic feats and his top running speed exceeds the speed of sound. In Werehog form, however, he loses this super-speed but gains tremendous brute strength. He can withstand multiple attacks from the toughest enemies and can dish out punishment in kind, savagely beating groups of foes into submission. In Werehog form, Sonic's arms are also capable of stretching great lengths. There's no sensible explanation for this ability, but it greatly increases his combat range and allows him to perform a number of acrobatic maneuvers that he would otherwise be incapable of.
It is also worth noting that during the Shattered World Crisis, other people became affected by the energy of Dark Gaia, showing darker sides of their personalities and acting in ways that would be completely out of character. Sonic, however, retained his true personality despite his transformation as his will is too strong for Dark Gaia to affect.