Lucina

Lucina is the future daughter of Chrom that made her debut as one of the main characters in Fire Emblem Awakening and appears as a playable character in Super Smash Bros. for Nintendo 3DS / Wii U, revealed in the same trailer as Robin, another character from Fire Emblem Awakening. In her game of origin, she initially appears disguised as a masked "Marth", having traveled through time to stop the awakening of the evil Fell Dragon Grima, helping Chrom's Shepherds on occasion and eventually joining them after revealing her identity. Lucina wields the Parallel Falchion, a reforged version of the same sword used by Marth and Chrom.

Super Smash Bros. for Nintendo 3DS / Wii U
Lucina is an unlockable character in both versions of Super Smash Bros. for Nintendo 3DS / Wii U. To unlock her in the Nintendo 3DS version, the player must either complete Classic Mode as Marth without the use of continues or play 40 Smash matches, then defeat her in a 1-stock match on the Arena Ferox stage. In the Wii U version, the player can unlock her by completing Classic Mode on Intensity 5.5 or higher or by playing 30 Smash matches, then defeating her in a 1-stock match on the Coliseum stage. She is voiced by Yū Kobayashi in the Japanese versions of the games, and by Laura Bailey in the English versions, both reprising their roles from Fire Emblem Awakening. She was originally meant to be an alternative costume for Marth, but was later made a separate character, the reason being that she has traits that differentiate her from Marth. Lucina is the only unlockable character that was announced before the Japanese release of the Nintendo 3DS version.

Lucina's moves are all shared with Marth: her neutral special is Shield Breaker, her up special is Dolphin Slash, her side special is Dancing Blade, her down special is Counter, and her Final Smash is Critical Hit. However, unlike Marth the damage output of her sword is balanced throughout, as opposed to Marth's dealing greater damage closer to the tip of the sword and less closer to the base.

Lucina's palette swaps are based on other female characters in Fire Emblem Awakening. In addition, one of her taunts has her briefly put on the mask she wears when disguised as "Marth", which is also used by Kirby when she is copied by him. Finally, Lucina has alternate victory quotes that have a chance of playing if she defeats either Marth or Ike.

Super Mario Maker
Lucina appears as a Costume Mario costume in Super Mario Maker. Her costume can be unlocked either by using her amiibo, or by completing 100 Mario Challenge on Expert difficulty or higher. Like the other Fire Emblem series character costumes, Lucina uses sound effects from Fire Emblem: Shadow Dragon and the Blade of Light. Pressing causes her to put her mask on.

Super Smash Bros. Ultimate
Lucina will return as a playable character in the game. This time, however, she'll act as one of three echo fighters in the game, the others being Princess Daisy and Dark Pit.

Trophy information
Red indicates the Trophy or description is exclusive to the 3DS version Blue indicates the Trophy or description is exclusive to the Wii U version.

Palutena's Guidance

 * Pit: That lady's moves are awfully similar to Marth's.
 * Palutena: That's Lucina. She used to introduce herself as Marth, so certain similarities seem inevitable.
 * Pit: What? She stole someone else's identity?
 * Viridi: Well, it wasn't quite like that.
 * Palutena: Marth had become a legend by her time—the Hero King. So Lucina took that name to bolster the morale of her own army. Think of it as a symbol of hope in the depths of despair.
 * Pit: That's pretty deep.
 * Viridi: You can't tell by looking at her, but I hear she's got a great sense of humor.
 * Pit: I'll try cracking a few jokes and see if that softens her up.
 * Palutena: The tip of her blade doesn't deal as much damage as Marth's. But her attacks are more balanced, even if they're not tremendously powerful.

amiibo

 * Lucina, from the Fire Emblem Awakening game, is Chrom's daughter and the future Princess of Ylisse. When she arrives from a doomed future seeking to prevent it from ever happening, she goes by the name Marth before her identity is revealed. She loves her father and would do anything to keep him safe.

Trivia

 * Lucina is the first (and currently only) female unlockable character in the Super Smash Bros. series, being unlockable in both versions of Super Smash Bros. for Nintendo 3DS / Wii U; all of the other unlockable characters, in addition to the ones from the previous three games, are male and gender-neutral (latter referring to Pokémon), not including Wendy O. Koopa who is unlocked as a pallet for Bowser Jr. in the 3DS version.
 * Like with her official appearance, Lucina's in-game model features the Mark of Naga on her left eye. Masahiro Sakurai has said that, as it is such a small detail, most players likely won't notice it during normal gameplay.