Marion works at the China Clay Workings. She is bubbly and friendly and loves digging, talking, and talking about digging. She is always ready to share her tales with the other locomotives, who sometimes try to avoid her. Thomas is always to happy to hear her stories. Items she has claimed to dig up in the past include a pirate chest. She enjoys playing "Guess What's in My Shovel", although the answer is almost always mud.
The morning after a large landslide at the clay pits, Marion met Thomas for the first time, scaring him with her bucket. When she introduced herself, Thomas found that she talked a lot. A few days later, she was still cleaning up the fallen rocks when Percy and James came her way trying to escape from another landslide caused by James' whistle. Although James escaped, Percy was swept up by the landslide. He was buried wheel-deep when he saw a large rock coming his way. It looked like the end for the little green tank engine, but Marion put her bucket in front of him and caught the rock, which she identified as the skull of a Megalosaurus.
Whilst repairing an embankment on the main line, Marion once hit a water pipe, causing a leak. Marion decided to cover up the leaky pipe, but Thomas later spotted water trickling out of the ground. When he took Marion to inspect the site, water gushed up from the ground and caused a landslide. Luckily, Marion was able to clear the line just before Gordon raced through with the Express. Marion promised that she would tell someone if she unearthed a water pipe in the future.
Later, Marion became worried when Ben didn't bring any coal to the clay pits. She was cross when she realised that the twins had used it all up, and got them to thank and apologise to Timothy, who came to the rescue by fetching more coal for Marion and the twins.
Some time later, during the construction of the Dinosaur Park, Marion was sleeping on a siding when Samson pulled a train of animatronic dinosaurs past her. She did not see Samson and believed the dinosaurs were real. She reversed all the way to Ulfstead Castle, and a few minutes later Samson arrived, revealing that the dinosaurs were in fact fake.
She was brought in to help with the construction of the new branch line. Upon meeting Bert, Rex and Mike, she believed that they were magical. She helped Alfie and Oliver dig part of the site when she discovered a buried treasure chest. She later attended the branchline's opening ceremony, and was surprised to discover that there are two Oliver's on Sodor.
Marion is very enthusiastic, and likes to think of herself as well-informed and is happy to share her knowledge. She is very talkative and loves to tell stories of her discoveries, however not all the engines prefer to stick around and hear her stories.
Despite her enthusiastic demeanour, however, she can also be rather stern, as seen when she told off Ben for not delivering any coal and making the twins apologize and thank Timothy.
- Marion does not have any front windows, making it difficult for her crew members to see.
- In the first trailer for Tale of the Brave, Marion's 3D Model lacked the protective corners on her main body. They were added on for the second trailer onward. Because of these being added, her lamp was moved slightly.
- Marion has a rear coupling hook, but her coal bunker is in the way to couple anything up to her. This implies that her bunker may be retractable.
- Marion's name is derived from her basis (the Marion Revolving Steam Shovel) as well as the company that built her (the Marion Power Shovel Company).
- Marion has never been seen with an operator or driver.