Marcus, who once was Damos's assistant, had come to resent Arceus due to his belief that it would allow Michina Town to return to being a wasteland if the Jewel of Life was reclaimed. This led Marcus to become the driving force behind Damos's apparent betrayal of it. By using his Bronzong's Hypnosis, he was able to control Damos and force him to destroy Arceus while not returning the Jewel of Life. However during the original turn of events, he had fallen to his death along with Damos after Arceus survived the attack and counterattacked.
After meeting up with Sheena, who had traveled to the past to stop Damos's apparent betrayal of Arceus, he learned how the future would have turned out as well as his own death. He then changed his plans to include silver water as well while attacking Arceus. This proved to be very effective and left the Alpha Pokémon helpless as the overall assault immobilized it. However, Sheena and Damos were able to communicate with the hearts of all the Pokémon, including Bronzong and Heatran, making them turn against Marcus, and Ash was able to make him give up the Jewel of Life by wrestling with him until he dropped it. As Ash caught the jewel and rushed with his Pikachu to return it to Arceus, Dawn, her Piplup, and another group consisting of a Chikorita, a Cyndaquil, a Totodile, and multiple Rattata, cornered Marcus, preventing him from following.
Even then, however, Marcus wasn't defeated yet. Although the Pokémon had stopped attacking and Ash had the Jewel of Life with Marcus unable to get it back, Arceus, now stranded at the bottom of the shrine, was by that time on the edge of death as the silver water continued to bury it. This, in turn, set off a strange sequence that nearly destroyed Ash, Brock, Dawn, Pikachu, Piplup, and Sheena, with Ash and Pikachu disappearing first as Marcus explained to Dawn what was going on.
At that moment, just as all seemed lost, Damos managed to reach the last remaining spark of life in Arceus's heart, giving it enough strength to reabsorb the Jewel of Life and fully recover, thus thwarting Marcus's plans and saving everyone from destruction (except Damos himself and a Pichu he befriended, who did not start disappearing). Marcus's scream was then heard and his crown seen on the ledge where he was standing, implying that he fell.
If he did, it did not kill him, since during the ending credits of the movie, it was revealed that Marcus had went on to work under Damos in cultivating the land.
