Characters more likely than you think: #4
Character: Celica
Universe: Fire Emblem
Debut: Fire Emblem Gaiden (1991)
Celica's History:
Celica debuted in Fire Emblem Gaiden for the Super Famicom in 1991 as one of the two protagonists. It was the second installment in the Fire Emblem series and was remade for Nintendo 3DS in 2017 as Fire Emblem Echoes: Shadows of Valentia.
Why Celica?:
Not only is Fire Emblem Gaiden the first sequel to the series, but its remake is now the most recent installment of the series and as a result, Celica is one of the few Fire Emblem heroes to make multiple appearances as a main character. She also appears as a playable character in Fire Emblem Warriors.
What makes Celica unique?:
Celica is a preistess. A class that is new to Super Smash Bros. She has the power of Fire, Seraphim, Thunder, Recover, and Aura. She has many other divine abilities as well, including shooting a beam of light from the tip of her sword upward into the sky, as well as the ability to spawn angel wings.
See 2:38 for her unique abilities.
It's not certain if a Fire Emblem 16 character will make a playable appearance in Super Smash Bros for Nintendo Switch, but it seems unlikely. If such is the case, Celica is nearly a shoo in.
Whether or not she will appear alongside Alm or if they will be separated once again is up for debate, but if either of them appear alone, Celica is both the more unique option and she has appeared alone in Fire Emblem Warriors.