- One biff! One bash!"
"And there's never a crash!"
- — Bash and Dash, Gordon and Ferdinand, fifteenth season
Bash and Dash are mischievous twins who always finish each other's sentences. They were sent to Misty Island because they were naughty on the Mainland, but now they always try to do their best for the Fat Controller.
In the fifteenth season, Toby became good friends with Bash and tried to find him a home on Sodor. Emily also became friends with Dash.
In the sixteenth season, they, along with Ferdinand, were sad because Ol' Wheezy was broken. They later laughed at Spencer when he did not know that Staffordwas not with him.
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. They are fuelled by wood and oil, instead of coal. They were originally sent to Misty Island for being naughty.
Living in an environment without proper rules, authority, or society, Bash, Dash and Ferdinand live 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's boiler, wheels and lining are painted slate grey and his cab and dome are painted amber. Dash's boiler, wheels and lining are painted amber and his cab and dome are painted slate grey. They both have a semi-circular symbol depicting three yellow trees with two brown axes crossing each other on the right sides of their cabs.