Because Thomas has pledged allegiance to Kurata, Marcus' fueled with a feeling of deep hatred in his heart to destroy his opponent at any cost that causes him to invoke a Dark-DNA Charge triggering on ShineGreymon to digivolve into Ruin Mode. Fortunately, Kristy arrives to stop Marcus, and he sees the error of his ways but is too late to stop ShineGreymon's rampage. Feeling hopeless, Marcus sheds tears streaming onto his digivice causing ShineGreymon to come into its senses and revert back to digi-egg.
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The Power of Destruction - ShineGreymon Runs Wild and we will let you know when it becomes available.