What kind would it be?
The classics are elements like fire or frost breath, but there can be other kinds that have effects. Maybe yours is a dragon of desire and can cause infatuation in even the most hardy of folk, or confusion, or sleep. Could be anything you want really, these are just fun things to consider. :3c
🤔 Hmm... GOT IT. Comfort breath. I would make a huge exhalation that leaves anyone touched by it feeling incredibly relaxed, warm, passive, and euphoric. Repeated exposure to the breath attack over a short amount of time, or exposure that's too intimate (such as a point blank breath attack kiss that forces the velvety magical mist down their throats) can actually cause the person's body to become so relaxed that their molecules become unstable and they begin to liquefy. It doesn't actually cause any harm to the individual(s) as it does wear off after a few hours and they re-solidify into their normal forms (granted, while being goop they probably oozed out of their clothing so they'll have to get dressed again). I like the idea that it could be used in a non-harmful offensive way to debilitate any foes, but also just as something to help friends de-stress regularly ^///^
a billowing cloud of glitter and social confidence