General Mechanics: Seraphine has cooldown on all on her down and side specials, in reference to the general mechanics of League and to prevent them being rapidly fired - and, pragmatically, to avoid her just buffing herself and debuffing her foes repeatedly. The cooldown meter is indicated by the moves having icons near her portrait.
She also maintains part of her passive, Stage Presence, where she collects four notes to gain range and damage to her basic attacks. However, in League of Legends, this is done by casting abilities near her allies. As she has no allies in Smash (without being in team battle), this seems to be a problem… but, thankfully, Seraphine can read peoples’ emotions, so she is truly everyone’s ally! Problem is that her opponents don’t know that yet, but that just means that she needs to inform them that they are her ally and she deeply cares about them… which she can do through her taunts! Every time a taunt is completed near an “ally,” Seraphine collects a musical note - gaining more if she taunts near more opponents. These spin around her and will expand her neutral attacks - her usual one magical spell can become a symphony as it is joined by extra notes, maintained by tapping the neutral attack button in a steady rhythm. Show the world what you can do~!
She does not maintain her echo ability, as I feel that’d be too OP in the world of Smash.
Neutral Special: High Note. Seraphine belts a high note, which fires forward as a magic attack. Like in League, it does more damage to opponents who are already at a high percentage. Strike them while they’re weak!
Down Special: Surround Sound. Seraphine sings a quick note, which forms a shield around her for a couple moments, slightly reducing damage. Once the shield disappears, Seraphine will have buffed movement, with this buff being stronger and lasting longer if she had been damaged while performing the move. Moreover, if she times it perfectly to block her attacker’s attack, then she’ll actually get a slight healing effect as well.
Side Special: Beat Drop. Seraphine fires a magical note out to the side. It damages enemies, along with slightly debuffing their speed for a few moments. If fired onto an enemy who is already debuffed (either by another Seraphine or an item like the Stopwatch), then it has a meteor effect.
Up Special: The Show Must Go Up. Based on the animation used in Encore, Seraphine belts a note as her platform rises up in a quick fluid movement, sending damage-inducing sound waves beneath her, similar to Robin’s up-special.
Jabs: Seraphine’s neutral attack fires one beam by default. It can be pressed repeatedly to keep firing the beams. As you build up music notes, these beams can be boosted to become multi-hit attacks that travel a longer range. She also has a natural rhythm to her attacks, with it being best to keep firing at a steady pace - A (or whatever button you use) rest A rest A rest, etc..
Smash Attacks: Encore. Seraphine’s ult turns into her Smash Attacks, which her charging up a powerful beam that fires out. As she’s a ranged fighter, this beam does not attract people to her like in the original game, as that would probably do more harm than good.
Aerials: Taking some liberties, her aerials all reference Dance Dance Revolution, like her mat is modelled after. She stomps down on the platform and an arrow fires out in that direction.
Like Bowser Junior, she loses her platform-dance-pad-thing (does it have a name?) when in free fall. This does make her lighter though, allowing for a slightly more controllable descent.
Taunts: In one, Seraphine waves and says “You inspire me!” In another, she does an excited two-arm cheer and declares that “You're all breathtaking!” In her third taunt, she just sits down on her board and poses mutely, so that people can use her taunt mechanic without verbally annoying the hell out of their friends.
Like Pit, she also reacts to being star-KO’d, dejectedly declaring that the “Shows not over…” Uniquely to her, she also has a chance of reacting to being brought back after being star-KO’d, musing to herself that she’s “Ready to sing again!”
Final Smash: Harominic Coordination. Similar to Mega Man, she fires a portal final smash that will toss captured opponents into a cutscene. In it, opponents end up standing in the middle of the rift, before being quickly surrounded on both sides. On one side, Ahri and Akali approach them and on the other they are caught by Evelynn and Kai'Sa. As they try to run into the Jungle, Seraphine emerges and they all attack the opponents at once, KO-ing at over 100% or launching otherwise. Uniquely, this Final Smash will change visually if she’s using her K/DA Superstar skin, with her allies also wearing their K/DA skins to match.