Lucina

Lucina is the future daughter of Chrom that made her debut 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 Fire Emblem representative. In her home game, 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.

Lucina was originally considered to be an alternative costume to Marth, much like Alph is to Captain Olimar, but ultimately, Super Smash Bros. director Masahiro Sakurai decided to make her a separate character. The reasoning for this is that he wanted some of her attacks to be significantly different to Marth's.

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. 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 Shield Breaker, her up special Dolphin Slash, her side special Dancing Blade, and her down special Counter. However, unlike Marth the attack output of her sword is balanced throughout rather than dealing the most damage at the tip. Lucina's palette swaps are based on other female characters in the Fire Emblem series.

Trophy information (Both Versions)
Red indicates exclusive to the 3DS version Blue indicates 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.

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).
 * Lucina is the only non-Mario Nintendo character playable in a Super Smash Bros. game to appear in a crossover with a third-party character playable in Smash; she appears alongside Ryu in the 3DS game Project X Zone 2.