Cosmo is one of the main members of Team Galactic and was selected as captain in 2019. He has so far competed in every single year of the Marblelympics.
In the 2017 Marblelympics, Cosmo finished 15th in Long jump and 7th in High jump, contributing to his team with a few points. He also competed in Fidget spinner collision, Relay run, Blockpushing, Steeplechase, and Archery with his team.
During the 2018 Winter Marblelympics, he finished 9th in Speed Skating (20m) and 12th in the Sand mogul race. He also competed in Halfpipe, Bobsleigh, Team pursuit, Curling, Gravitrax Biathlon and Hockey with his teammates.
In 2019, Cosmo was awarded the captain role. Cosmo competed individually in the second event of the MarbleLympics, funnel spinning, and finished 6th after qualifying for the final. In the sand rally, he stayed near the front of the pack for the entirety of the race and, with a great burst of speed at the very end, managed to win his first medal, a silver. He also competed in Balancing, Slalom, Relay Race, Block Pushing, Hubelino Maze, Rafting, and Collision with his teammates.
Long overdue, Cosmo won his first ever individual medal in the 2019 Sand Rally event by placing 2nd. Although he never held the lead in the race, he was always near the front of the pack, and put together a great burst of speed to overtake several marbles in the final stretch of the race. He also has two additional silvers that he won with his team from the 2018 Bobsleigh and the 2019 Block Pushing.
For the 2019 Marblelympics, Cosmo was awarded the captain role, despite at the time not having any individual medals to his name. This caused some controversy, as many fans believed that the more successful Starry should have been chosen. However, due to his silver medal in the 2019 final event, it seems that fans have restored their faith in him, and most of the controversy has since died down.