Some folks have asked me why I ship these two so I’ll just put a quick version of why I do here:
 
As usual with me a lot of this comes from personal headcanon and fanfiction (written or being written by me).
 
This is a situation of two immature people seperating, becoming more mature and meeting up again years later. Being childhood, lets say, on again-off again friends. They decide to rekindle that friendship and learn more about each other, accompanied by a healthy competitive streak to keep things interesting.
 
Of course I have to do things with Dumbbell’s character, for instance giving his cutie mark a meaning. I decided on a double meaning. So long story short, he lifts.(lol) He lifts spirits, he can bear heavy burdens, and he can probably kill you with a head-butt. He is a trainer.
 
And my headcanons for him, being a pony who has traveled for long periods of time outside of Equestria, (that in and of itself is a whole other headcanon rabbit hole involving Gilda.) experiencing the crap hole that is apparently the rest of the world would prepare him for any rinky dink emotional trauma a pony might have.
 
This also worked with how I planned on pairing him up with Rainbow Dash since she’s immature about most things. Being athletic himself, Dumbbell might become that confidant role she needs. Dash is a proud pony and secretive about her insecurities. The deeper the personal issue the harder it is to get her to confess or air out her issues especially to her friends. But Dumbbell would provide a comfortable outsider option and the fun thing for me is building up that trust between them.
 
The reason why he was a jerk to her in the best young flyers competition ep is because old habits die hard. They picked on each other a lot back in flight school.