Bash and Dash are fun loving steam engine twins who live on Misty Island, with Ferdinand.
Bash and Dash are the wacky, mischievous Logging Loco twin engines who know each other so well that they can often finish the others' sentences. Living in an environment without proper rules, authority, or society, Bash, Dash and Ferdinand lived for fun, silly games and playing about in the chaotic, consequence-free Logging Camp and the dense Jobi forests of Misty Island. Often, they were easily distracted, reckless and got very little work done and when they did work, it was in a particularly silly, wacky, or questionable manner.
However, after Thomas wound up on Misty Island, later managing to make his way back to Sodor, the twins were welcomed to the railway by the Fat Controller. The Logging Locos' outlook has now changed and they all try to be Really Useful engines.
Instead of aspiring to only goof around, they are now keen to help the Sodor engines and learn about the proper way of doing things, the values of good behaviour and forming new friendships with others. Although sometimes Bash, Dash and Ferdinand may be baffled by concepts that are unfamiliar to them, due to living in isolation on Misty Island for some time, they attempt to assimilate new prospects, take part and strengthen their friendships with the Sodor engines and their reputation of being really fun.
Joining in or even trying to recreate these previously unfamiliar social quirks helps the kooky Logging Locos learn about the world around them, the virtues and graces of others and how to appreciate and understand new things to help them be Really Useful.
Although they will always be fun-loving and may raise the eyebrows of some of the bigger engines as they lark about with their work, the Logging Locos' new-found respect for considering others and learning and applying everyday rules, values and behaviours helps them to learn and draw from the Sodor engines and the sensibilities of society, the world around them and maturing into Really Useful engines to make the Fat Controller proud.
Bash appears to be the more timid, peaceful one of the twins, while Dash is more outgoing and supportive.
Bash and Dash are based on the Bear Harbor Lumber Company's locomotive #1. This type of engine is known as a "gypsy", which had a special yarding mechanism at the engine's front, allowing it to haul logs when the gear is engaged. However, Bash and Dash's yarding mechanism is behind their cabs instead of their fronts to accommodate their faces. Their driving gears and brakes have been removed entirely and they have screwlink couplings. Their cabs appear to be much sturdier, as opposed to the "open" cab that their real life counterpart possesses.
- Bash and Dash can run on either wood or oil.
- Due to the excessive modifications from their original prototype, neither Bash nor Dash would be able to run in real life; there is no visible means as to how their cylinders turn their wheels at all.
- Bash and Dash have only been partially modified for British railways, with screwlink couplings but no buffers.
- In a promo of Dash, his siderods are missing. A CGI head-on promo of both twins also depict them with their faces swapped.
- Dash's livery is the same as his twin's, but with the placements swapped.
- Dash has more merchandise represention than Bash, a first-timer in the franchise.