You can’t promote anyone else to Dancer in Engage
Fire Emblem Engage continues the tradition of unique character classes, Dancer included. You’ll need to make it through a fair bit of Engage to actually acquire a Dancer, and even then, it comes with caveats. Thankfully, that very Dancer (Seadall) is a pretty cool addition to the game, and serves multiple roles.
You’ll find Seadall, the lone dancer, at Chapter 15: Dancer in the Ruins
As the first male Dancer character in the series, Seadall is unique out of the gate. You’ll meet Seadall in Chapter 15 during the mission itself (where you will recruit them permanently). The phrase “Dancer in the Ruins” is a pretty big hint!
As is the case for many years running, Dancers provide a support-based role for the party, buffing stats for other units and wielding some tricks of their own (especially with the Engage system in play).
Seadall will also give you tarot readings (Fortune Telling) at the Somniel
After having Seadall join your team, they’ll set up in the Somniel, near the poolside (Seadall’s exact location can be found in the gallery above).
In addition to bringing them into battle, you can also talk to them in the Somniel hub, give them gifts, and get a tarot reading. Triggering the latter activity will allow you to select a party member for a reading: revealing another person with whom they are more apt to bond with. If you want, you can optionally bring those two in battle to supercharge bonds. Think of it like an extra set of rules you can impose on yourself (bringing in specific party members) while you boost your bonds in the process.