An Echo Fighter (ダッシュファイター Dash Fighter ) is a playable character in the Super Smash Bros. series, that uses a moveset and physics which are considerably similar if not identical to that of another character. The concept has been around since the original game, but it was not until Super Smash Bros. Ultimate that the term "Echo Fighter" was coined. Fans of the series previously referred to such characters as clones, although not all clones (such as Dr. Mario or Pichu) are officially classified as Echo Fighters.
Each Echo Fighter is marked in Ultimate with an Epsilon (ε) symbol internationally, and a prime (′) symbol in Japanese, while sharing their base fighter's number. On the character selection screen, there is the option to stack Echo Fighters with their base fighters, or keep them separate.
None of the five downloadable characters planned for Ultimate will be Echo Fighters.
Dark Samus, debuting in Ultimate, is an Echo Fighter based on Samus. She is the only Echo Fighter to be based on one of the "perfect-attendance crew", or the twelve characters that have appeared in every Smash game in the series. Therefore, she is also the first Echo Fighter of a starter character, as only the original twelve are available by default in Ultimate.
While her fighting moves are primarily copied from Samus, Dark Samus's animations have a number of key differences. As with the Metroid Prime series, Dark Samus constantly hovers in place instead of standing or walking, although she will plant her feet on the ground for certain attacks. Dark Samus charges and fires her Charge Shot with a single hand, whereas Samus stabilizes her Arm Cannon with her left hand. The Charge Shot has a darker appearance as well, as does her Final Smash, Phazon Laser. In Dark Samus's case, she does perform a similar attack, at the end of Metroid Prime 2: Echoes, whereas Samus's Zero Laser's origins are ambiguous. Finally, Dark Samus does not morph when dodging or rolling, she shares her victory theme with Ridley (a more sinister version of the Item Acquisition Fanfare), and her taunts and victory poses are different from Samus.
Dark Samus and Daisy are the only two characters to be Echo Fighters of a female fighter. Similarly, Peach and Samus have had alternate costumes based on Daisy and Dark Samus in previous titles. These were removed in Ultimate. Dark Samus is the only Echo Fighter who is an antagonist and who shares the same star KO sound as her base character, and is one of two Echo Fighters (alongside Dark Pit) to be an actual clone of her base character in her home series.