Von den Metarex geht eine Strahlung aus, die allen anderen die Lebensenergie entzieht. Nur Cosmo kann dieser Macht widerstehen, weil sie zum gleichen Pflanzenstamm wie Dark Oak gehört. Um ihre Freunde und Sonic zu retten, benutzt sie ihr Amulett mit den Geheimkräften. Und wirklich bekommen sie langsam ihre Energie wieder. Nun gehen sie gemeinsam den Kampf gegen Dark Oak an.
When the giant seed finally reaches the final stage of its metamorphosis and starts sucking the life out of everyone except for Cosmo, she takes the Chaos Emeralds to Eggman, thinking that he'll know what to do. Unfortunately, Dark Oak attacks Cosmo, who drops the Chaos Emeralds into space. Thankfully, they close in on Sonic and Shadow, who use them to transform into Super Sonic and Super Shadow and attack the Metarex seed. But, once they destroy it, they reveal an even smaller planet with a gravitational force that could potentially destroy the whole galaxy!
Cosmo feels helpless but her mother, in her mind, assures her that she is the one who will save the galaxy. She then transforms into a new form and becomes determined to stop this once and for all. She flies over to the planet, passes through the gravitational force that neither Super Sonic nor Super Shadow could pass through, and plants herself on top of it. She then becomes a tree, saying that she has now immobilized Dark Oak. She tells Tails to load and fire the Sonic Driver and shoot it at the planet. Everyone is shocked and does not know whether or not to risk saving the galaxy if they're going to kill Cosmo in the process. Tails, however, is very hesitant, but Cosmo re-assures him that her seeds will be spread throughout the galaxy. He then thinks back to all of the good times they've had and their love and, tearfully, fires Super Sonic and Super Shadow at the planet, completely destroying it. Tails and Cosmo, during the ending sequence (which was cut from the English dub), say farwell to each other. At the very end as Cosmo floats off, she says "I love you."
Cuando la semilla gigante finalmente alcanza la etapa final de su metamorfosis y comienza a chupar la vida de todos excepto de Cosmo, ella le lleva las Chaos Emeralds a Eggman, pensando que él sabrá qué hacer.
