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For those at this point in the game, congratulations on reaching the finale ofSonic X Shadow Generations. You’ve taken down all the rival bosses (Metal Sonic,Shadow the HedgehogandSilver the Hedgehog) and three main bosses (Death Egg Robot,Perfect Chaosand Egg Dragoon), with only one more standing in your way. The Time Eater has been the main antagonist of the story, having been the one who brought everyone into the White Space, and now is Sonic’s chance to get everyone back home.
After collecting all the Chaos Emeralds, Sonic and Tails (Modern and Classic) confront the Time Eater, who has been being controlled by Classic and Modern Eggman the whole time. It was Modern Eggman that found the earlier form of the Time Eater after the events of Sonic Colors. Having recognized its powers, he wanted to use it for his own good and sought out the chance to get someone as smart as him to help out with his plan: the Classic version of himself. As the Sonics begin to attack, they underestimate its brutal force, and are taken down quickly.

Sonic X Shadow Generations: Ending Explained
Sonic X Shadow Generations endings are bittersweet.
With the support of Sonic’s friends that he helped and fought against throughout the game, alongside the power of the Chaos Emeralds, both Sonics transform into Super Sonics. The battle thus begins within a time wormhole where the Sonics will face off against the Time Eater once and for all. Something unique about this battle is that players can switch between Modern and Classic Sonic, with each of them having their own attack: Modern withSuper Sonic Missileand Classic Sonic withAtomic Spin.
As you chase down Time Eater, it will begin to attack Sonic with a wave of homing missiles, which can be avoided by usingQuick Step. The Eggmans will hatch a plan to move outside the wormhole, making it hard to attack while usingModern Sonic. Switch toClassic Sonic, which will change the perspective to 2D and push the Sonics outside, making it easier to send missiles at Time Eater. Once you go back into the wormhole, Time Eater will use portals to attack Sonic with its upper arms, which can be avoided by simply moving out of the way.

For the portal attacks, you can move outside the wormhole if time permits.
Sonic X Shadow Generations: Biolizard Boss Guide
Boiling the boss battle down to a science in Sonic X Shadow Generations.
Slowly move closer to Time Eater and once the lock-on target becomes seen on the core, boost towards it and attack until it cracks. Reap the rewards of the Rings that spill out, since you will have to repeat this cycle again. After attacking the core again, Time Eater will lose his lower limbs but also gain new attacks, such as firing a giant laser. Luckily for you, this laser takes time to charge, so be prepared to switch Sonics when the laser fires. Another attack will slow down time and send out homing missiles from a distance, so once time goes back to normal, avoid those incoming attacks.

After hitting the Time Eater’s core once more, it will unleash a giant fireball at the Sonics, which, by the looks of it, is way too big to avoid. To counter this move,press and holdLB/RB or L1/R1at the same time. This will make the two Sonics combine their superpowers to boost straight through Time Eater’s core. The battle ends with Modern Sonic and the gang, including Classic Sonic and Tails, returning to his party. The Sonics’ will converse for a bit before they go back to their respective generation. Sonic tells them as they leave that they’ve got a great future ahead of them.
Sonic X Shadow Generations

