Zach Aguilar and Jeannie Tirado, who respectively voiced the male and female versions of Byleth in Fire Emblem: Three Houses and Fire Emblem Heroes, reprise their roles in the overseas version, while Yūsuke Kobayashi and Shizuka Itō reprise their respective male and female roles in the Japanese version.
As mentioned by Masahiro Sakurai during the January 16, 2020 presentation, Byleth is specifically designed to be a "distance demon," a character such as Marth or Shulk who utilizes large hitboxes to zone out opponents at mid-range. Boasting a variety of weapons, Byleth's overall reach is fittingly long in line with his archetype, and his attacks are generally very strong; to compensate for this, Byleth has poor overall mobility, high startup and ending lag on many of his moves, and a rather short grab range. All of this makes Byleth's general gameplan very patient, which reflects on his position as a "teacher" or "professor" in his game of origin: his sluggishness makes it necessary for him to plan ahead and learn the opponent's habits, before covering their options with his range and arsenal of hard-hitting weapons.
Like other weapon users, Byleth's attacks have disjointed hitboxes that allow combat to be at a safe distance. Neutral attack is a quick chain of attacks that act as a standard get-off-me option, especially due to the speed of Byleth's moveset. The third hit of neutral attack is good for sending opponents away, and the infinite is a good damage racker that can KO at high percents near the edge. Byleth's tilts all use the Sword of the Creator. Up and forward tilts have wide hitboxes and decent speed, making them effective spacing attacks. Down tilt is a whip with the sword in chain form, giving it more effective distance and allowing it to combo into aerials. Finally, dash attack is a wide swipe forward, which allows it to punish whiffs but is also easily punishable itself. All of Byleth's up attacks emphasize the Sword of the Creator's extended chain form; up aerial causes him to lash upwards in a flurry, dealing multiple hits and acts as a good tool to deny landings or start a juggle. Its looping hits can also drag opponents downwards to initiate extended combos. Byleth's up special causes him to thrust the chain upwards to grab opponents or ledges. As a combat move, this up special can combo from certain moves, and causes an untechable meteor smash at high percentages; if used on offstage opponents, Byleth will hop off the opponent's head for a meteor smash, which can cause an unavoidable KO at high percents. This hop also has extremely low ending lag, allowing for certain followups like side special; in very specific cases, it can even zero-to-death (on Donkey Kong). As a recovery move, the sword grants Byleth a very long tether recovery, which can grab Battlefield's ledges as low as near the bottom blast line. Notably, Byleth's up special can attach to walls and perform a wall jump if it touches a wall, much like tether recoveries in Melee. Altogether, these traits provide Byleth with a safe array of covering various approach options.
Byleth's other weapons grant more specialized options. Areadbhar, a lance, is used for Byleth's side moves (forward smash, forward aerial and back aerial, and side special); it has long range and uses a tipper mechanic that deals more damage at the tip of the lance. Forward smash is a slow but long-ranged stab that deals more knockback if aimed upward and tippered, allowing it to heavily punish jump options. If aimed downwards, the lance can also hit opponents grabbing ledges. Meanwhile, forward and back aerials are very effective spacing moves, even outranging those of Marth, and the tippers deal heavy knockback. Byleth's side special has him swing Areadbhar in a slow, but wide swing, and allows him to step forward if the special button is held. Its massive hitbox easily denies jump options and acts as a powerful but risky spacing option. However, all of Areadbhar's moves are very weak if the hilt lands, so proper spacing is vital; this is especially important with side special, as the sourspot deals extremely low knockback, making it possible for opponents to punish Byleth at low percents even if it lands.
Aymr, an axe, is used for Byleth's down moves (down smash, down aerial, down special); it is an extremely slow, yet powerful weapon that deals high damage and knockback on all moves that use it. Down smash is slow overall, but hits very hard and can KO as early as 90%. Down aerial is a similarly slow swing downwards with extreme landing lag, but it is the strongest meteor smash in the game when it lands, making it also among the most rewarding. Finally, Byleth's down special causes him to charge Aymr in a super armored stance, before unleashing a powerful, Special Zoom-inducing swing. It allows Byleth to pass through platforms and turn around in the opposite direction while charging, which can be used for mindgames. It also has a surprisingly wide hitbox that starts behind Byleth's head, making it much like Warlock Punch; a high-risk, high-reward move that can catch opponents by surprise.
Finally, Failnaught is a bow which is used for Byleth's neutral moves (neutral aerial and neutral special). Neutral aerial is a long-lasting, wide-ranged spinning move much like Palutena's, making it a good option out of shield due to its fast startup, and can also initiate combos or edgeguard with its looping hits. Byleth's neutral special also charges up Failnaught with an arrow, which can be shot at two different strengths: a slow but strong arrow that acts as a sniping option and passable spacing projectile, or a very delayed shot that acts as one of the strongest projectiles in the game, which can also almost break a full shield. The charged projectile also becomes an energy projectile, making it possible to absorb it, but not inhaled nor Pocketed. Unlike every Link's respective Bows, Byleth can cancel Failnaught's charge before he reaches the delayed charge shot, though he is unable to cancel it after he reaches that point. Byleth's neutral special can also turn around before the delayed charge shot.
Byleth is not without flaws, however. Due to his mobility being among the worst in Ultimate, his approach is very committal. This flaw is further stressed due to many attacks having slow startup (e.g. down smash/down aerial), narrow hitbox placements (e.g. forward/back aerials), or even both (e.g. forward smash). His dash attack, neutral aerial and side special are exceptions, but are easily punishable on shield due to their ending lag, while the lattermost is dangerously unsafe if the sweetspot does not land. This flaw becomes even more dangerous with Failnaught’s unique charge properties, as while the arrows fired from it are powerful and fast, they are equally as dangerous if reflected as Byleth cannot cancel the move after charging it halfway through. Byleth’s abundance of KO options is also a double-edged sword, as while it makes it easy for him to heavily punish mistakes, it also makes counterattacks an excellent option to punish his many KO options if used frequently.
Byleth’s grab game is also flawed. While he has an up throw that deals passable damage, a capable 0% combo starter in down throw, and a high-percentage kill option with his forward throw, his pummel is very slow and his throws in general are ineffective for starting combos due to high base knockback. When combined with his short grab, Byleth’s grab game is only useful at point blank range, and typically used to deal damage if other moves stale.
Finally, even though Byleth has a large array of KO moves, they are not always reliable. His up smash, like certain other multi-hitting up smashes, has almost no grounded hitboxes, making it ineffective against grounded opponents. His side and up special moves have strict hitboxes that only work from a specific horizontal distance or above Byleth, respectively. His down special, despite its aforementioned strengths, is very punishable due to its startup and ending lag throughout, leaving Byleth very vulnerable to grabs. Lastly, his most reliable KO moves will only KO starting after high percentages, making it tough for him to KO effectively.
All in all, Byleth is a ranged powerhouse with great offensive potential due to his weaponry, which comes with varying uses depending on each weapon. Byleth's arsenal grants him access to a mixture of highly damaging attacks, KO options, combos, and setups. However, Byleth's slow mobility and poor overall frame data renders his approach strategic, requiring the player to be very patient with their opponent and read and punish their mistakes, as a careless move on Byleth's end will easily give his opponent just as big of an opening.
For a gallery of Byleth's hitboxes, see here.
Note: All numbers are listed as base damage, without the 1v1 multiplier.
In competitive play
As per usual with any recently released character, it is hard to say where Byleth stands in terms of viability. Some pros have stated the character looks promising, including MkLeo. Both Leo and Pink Fresh were able to take 1st place at their respective locals with the character. However, other pro players believe the character is not as promising, mainly citing the character's poor frame data, slow ground and aerial speed, and limited landing options as huge drawbacks. Many have noted how Byleth struggles against faster characters such as Fox and Pikachu.
Any number following the Smasher name indicates placement on the Fall 2019 PGRU, which recognizes the official top 50 players in the world in Super Smash Bros. Ultimate from July 13th, 2019 to December 15th, 2019.
Classic Mode: A Heroic Legacy
Byleth's Classic Mode route is themed around the Fire Emblem fighters and stages from across the Smash series, fought in order of release year. All battles are stamina battles and the player always starts with 100 HP.
Role in World of Light
Due to his status as downloadable content, Byleth does not have a legitimate role in World of Light. Instead, he is unlocked for use in the mode after freeing 10 fighters from Galeem's control. If loading an existing save file that meets this condition before downloading Byleth, he is immediately unlocked.
Male Byleth's Fighter Spirit can be obtained by completing Classic Mode. It is only available periodically for purchase in the shop for 300 coins, but only after Byleth has been downloaded. Unlocking Byleth in World of Light allows the player to preview the first spirit below in the Spirit List under the name "???". As a Fighter Spirit, they cannot be used in Spirit Battles and are purely aesthetic. Female Byleth has a Fighter Spirit of her own, available through the shop. Each Fighter Spirit has an alternate version that replaces it with its artwork in Ultimate.
In Spirit battles
As the main opponent
As a minion