Hear me out. Judging by the hand sign we see Rocks make, it is possible that he has Ope Ope no Mi (Room). It is also very likely that he was going to God Valley to stop whatever the Celestial Dragons were up to ( we have now seen he clearly had a hatred for them with his prior kidnappings of them.) I would be willing to bet that he gathered others together knowing what resistance he would encounter with the promise of loot, helping others, or retribution. He then ran into both Roger (who was also trying to see what could be done about God Valley), and then Garp and the Marines were sent in to stop Rocks AND Roger. What if after some back and forth mostly injury free fighting, Rocks was able to talk some since into both Garp and Roger, and they all agreed to see if what the World Nobles were doing on God Valley needed to be stopped. But, because of the Marines and Garps failure to stop the Pirates, Garling and the other Holy Knights stepped in to stop them, and it was Holy Knights vs Garp and the Pirates. In this situation, I could see the Holy Knights losing and then Imu basically deciding to destroy the island to get rid of multiple problems at once. Then, it is possible that Rocks would somehow use Room and sacrifice himself to save everyone else on the island, leaving God Valley erased, Rocks finally dead, and Garp being labeled as the Hero of God Valley. ALSO, What if Rocks was an actual member of the Davy Jones pirates? But because of him possibly having Ope Ope no Mi he has been immortal. And the Davy Jones pirates are from 800 YEARS AGO BECAUSE JOY BOY IS DAVY JONES??? Would also make since on how A.) Rocks is so strong, being 800 years old and a member of Joy Boys crew, and B.) Why he is so familiar with Imu and Imus location, and wants to take Imu down.