Inspired by this thingy: https://s.castle.xyz/h3iSuARBqpCQ

Similar to the Duke dogs. The Duke dogs (formally, GWR "Earl" class) were locomotives built in the same year of Mallard, around 1930s. They used Duke's boiler and bulldog's frame. They were a success and one remained preserved. It's a 4-4-0 with inside cylinders, and it's one of the only standard gauge locomotives to have outer frames.