Miscellaneous stuff:
To start things off, I'll mention that I feel Micaiah should be a middle height lightweight. She should be shorter than Ike but taller than Mario and she doesn't wear armor or have heavy weapons nor is she large herself so the light weight makes sense.
For palettes, we'll assume she'll have 8. Her first would be her Light Mage outfit
https://vignette.wikia.nocookie.net...est/scale-to-width-down/250?cb=20160930101019
Her second outfit would be her Light Sage outfit
http://fireemblem.wikia.com/wiki/File:Lightsage.PNG
Her third would be her Light Priestess outfit
http://fireemblem.wikia.com/wiki/File:Ike_and_Yune_in_the_final_battle.png
Her fourth would be based on Sothe's Rogue outfit
https://vignette.wikia.nocookie.net...est/scale-to-width-down/280?cb=20160930101401 Optional whether her hair changes colour though I'd personally keep it silver (helps since her Boxing Ring title could literally be Silver Haired Maiden although there are other names that work)
Her fifth would be based on the armor of a Daein soldier
https://youtu.be/b3yjuq4QYNk?t=29m3s
Her sixth would be based on Sanaki
https://vignette.wikia.nocookie.net...est/scale-to-width-down/290?cb=20180502004212
Her seventh would be based on the herons Rafiel, Leanne and Reyson
https://vignette.wikia.nocookie.net...est/scale-to-width-down/350?cb=20170508093504
And her eighth outfit would be based on Yune
https://vignette.wikia.nocookie.net...est/scale-to-width-down/285?cb=20130113134233
I feel these 8 work rather well as they're all based on things tied to Micaiah (her 3 classes, her 'boyfriend' for lack of a better word, her countrymen, her sister, the laguz she has the closest tie to and the goddess that accompanies her) and she gets proper outfits for team battles with the Light Mage and Sanaki outfits being red, the Light Sage having blue in it and the Sothe outfit having green in it. And there's even yellow thanks to Yune's outfit.
Another potential outfit could be one based on Sephiran.
https://vignette.wikia.nocookie.net...est/scale-to-width-down/289?cb=20151018000605 The reason for Sephiran is he is Micaiah's ancestor.
Her stage appearance could be warp magic. Unoriginal, I know since all other FE characters save for Corrin use it but it makes sense for Micaiah given that she's a mage.
One of her walk animations is based on her walk animation during chapters
https://youtu.be/ig7a_nULdDc?t=4m55s The uploader changes the speed to max like a sane person afterwards so I can't show it off outside of that cutscene. Characters in Smash also have more than one walk animation so Micaiah would require some unique ones made.
Her run animation is based on her run in the opening cutscene of Radiant Dawn
https://youtu.be/ig7a_nULdDc?t=3m18s
Her lying down on back animation could be based on when she gets knocked down
https://youtu.be/dLoNkLC5FIU?t=21s Lying down on front animation would have to be original.
Her crouch animation would be similar to Zelda's, going off the opening cutscene of RD again.
https://youtu.be/2m_-WjCdIBg?t=8m36s Micaiah would not have a crawl.
Micaiah would have low movement speed much like how she's slow in RD. Plus I envision her as having a turtler playstyle.
Sleep animation would be similar to Marth's, having Micaiah kneel down and supporting herself with her staff.
Ledge grab animation would be Micaiah holding herself up with both hands. Ledge attack would be her pulling herself up and jabbing out her staff.
Both get up attack animations would have Micaiah hit to one side and then the other with her staff.
Normal grounded attacks:
Her jab combo would be a basic 2 hit combo with her staff, the first hit being an upward swing based on Mist's staff attack animation
https://youtu.be/dLoNkLC5FIU?t=9m16s and the second hit would be a higher up hit based on the regular staff attack animation.
https://youtu.be/dLoNkLC5FIU?t=6m18s This jab would be like Samus' where it doesn't connect fully until higher percents, the first hit would knock the opponent up while the second knocks them away, allowing Micaiah to continue attacking from afar with her spells. One could also choose not to do the second hit to attempt to follow up into a different attack.
Her forward tilt would have her turn her staff to make the bottom face the same direction she's facing and have her jab it outwards. This tilt would be primarily for trying to keep the opponent out so Micaiah could continue to attack at long range. Could also lead to tech chase scenarios, especially with Purge.
Her down tilt would be a kick, similar to Zelda's or Ryu's strong down tilt and would pop the opponent up, allowing for combos.
Her up tilt would be a quick swipe upwards with her staff, being a decently disjointed hitbox to anti air with and having low enough endlag to allow for combos at low percents. Horizontal range would be poor but would cover directly in front of and behind her.
Her smash attack charging animations could be based on her critical animations
https://youtu.be/dLoNkLC5FIU?t=31s
Forward smash would be Micaiah casting Shine in front of her. There would be a sweetspot at the middle of the spell and as the move spreads outwards, it would get weaker.
Down smash would be her casting 2 Light or Ellight spells on both sides of her (so think Megaman's down smash but the hitboxes start above Micaiah and come down beside her).
Up smash is similar to Mewtwo's but a single hit instead of multihit. Based on the spell she uses in the opening cutscene of Radiant Dawn
https://youtu.be/ig7a_nULdDc?t=3m5s
Dash attack would be a twirl before striking with the staff. Specifically thinking a backhand strike with it as that seems the quickest and most natural option out of a twirl. Would have a short burst as she starts the twirl before quickly stopping.
Aerials:
Neutral air would be a quick twirl as Micaiah releases light magic, hitting all around her. Would have a semi spike angle.
Forward air would be an overhead swing with the staff complete with Micaiah doing a somersault (think Rosalina's forward air but in the opposite direction).
Back air would have her strike behind her with the butt end of her staff. Thinking something like Pit's back air but with more range.
Up air would be a quick light spell, appearing a decent distance above Micaiah before finishing. Due to the nature of this move, if it's done while she's falling, it'll end roughly where she was (less so if she's fast falling) and if she's jumping while she uses it, the spell will actually envelope her as the spell forms above and descends before ending.
Down air would be a downward vertical swing with the staff with the tip of the staff having a meteor effect. Think similar animation to Ike's, Roy's and King Dedede's down air. Rest of the staff would send horizontally away.
Specials:
Her neutral special would be magic charging like Robin's but she won't have weapon durability to deal with and the spells will behave like they do in RD, coming from above at specific distances. The spells she would use are Light at first then Ellight then Thani and lastly Purge. Light would be a simple, quick single hit that would hit very close to in front of Micaiah and would just knock the opponent away. Ellight would be a multihit that would hit a little further away but would send the opponent towards Micaiah, allowing for combos. Thani would hit around the same range as Ellight, would be a single hit and would either ignore shields like the customs for Little Mac's side special and Meta Knight's down special or would do heavy shield damage. Purge would hit the furthest away and would take the longest to cast. During the casting animation, a reticle would appear at the Ellight/Thani range and can be moved further away from Micaiah if needed to hit enemies further away. Because the spells follow the RD animations, they can be used while onstage to hamper opponents offstage or can be used while Micaiah is on a platform to hamper those below her.
Side special could be a few things. It could be Silence where Micaiah uses it at a certain range and if it connects with the opponent, they lose access to their specials for a short time. It could be Sleep, being basically the same thing but putting the opponent to sleep instead. Would have no effect on aerial opponents. It could also be Rescue, putting a unique twist on the staff by using it as an offensive move to force the opponent close to Micaiah. There's also the option for the move to cycle between these options at random or in a specific order like Peach's forward smash. If customs come back, these other options could be her customs. To clarify on the Rescue idea, I know I put emphasis on Micaiah being a long range fighter and so bringing the opponent closer may sound counterintuitive but there are some characters that would do a better job camping than Micaiah which would force her to approach. The Rescue staff could help with this. I'm also thinking she could do some cool combos like ftilt to send the opponent away, Rescue to bring them back while still in hitstun and then something like jab or up tilt or whatever to finish or extend the combo.
Her up special would be Rewarp, making it similar to Palutena's, Mewtwo's and Zelda's up specials. If that's deemed too similar to the others, a hitbox could be added to her reappearance (but not her initial warp) either as a simple means of defense against those who attempt to hit her out of her recovery or as a tricky means of offense.
Down special would be Rescue/Guard. Basically, Micaiah would defend herself with her staff and if she's hit, Sothe will warp to her, take the hit and slash at the opponent. In other words, a fancy looking counter. Unoriginal in concept but in execution, it's not just another 'enter a fancy stance and then hit the opponent' and it actually has proper context given the bond Micaiah and Sothe have.
Her Final Smash would be a variation of Robin's. She would use the Rescue staff to bring Sothe to her who would then dash forward a distance before either hitting an opponent or warping away, similar to what Chrom does. After the initial hit, Sothe would slash at the opponent repeatedly while Micaiah charges up Rexaura before having the spell hit the opponent. Additional effects that could be added are the screen blacking out and slashing animations appearing before the spell brightens up the screen again to reference Sothe's Bane and a small but neat detail that could be added is Micaiah having red eyes like when Yune takes over her body.
Grabs and throws:
Micaiah would grab with magic much like Robin as she will always have a tome and a staff inhand. Could possibly give her a tether grab with the Rescue staff or even a disjointed grab where the grab box doesn't appear next to her but rather a distance away, much like Robin's Distant Nosferatu custom, putting further emphasis on Micaiah excelling at long range combat and not doing well at close range. If that's too much of a hindrance, she could have a small normal grab range along with her disjointed Rescue grab or she could just have a proper grab with magic.
Pummel would be unique. Pressing attack while grabbing an opponent will have Micaiah use Nosferatu, healing herself and damaging the opponent. This would be a slow pummel due to the value of healing. The damage and therefore healing rate could be anywhere from 1-3% or could scale based on Micaiah's percent and her opponent's much like how Robin's down special works. To further make her pummel special, pressing special while grabbing an opponent will have Micaiah use Sacrifice on them, healing the opponent and damaging Micaiah herself.
An adorable idea I had for her forward throw would be a clumsy push. This would be based on the opening cutscene of RD and would show how she isn't much of a physical fighter.
https://youtu.be/2m_-WjCdIBg?t=8m43s
Back throw could either be using magic to powerfully send the opponent away like Robin, Ness and Mewtwo or she could send the opponent behind her before jabbing them with the end of her staff.
I have two ideas for down throw. One is where she puts the opponent onto the ground and twists the bottom of her staff onto the opponent before they're launched. The other is having her slam the opponent into the ground as she uses Rescue on Sothe to have him land on the opponent either with a stomp or a slash before he warps out.
Her up throw would have her throw the opponent up as she sticks her staff up, having the opponent land on the staff as she thrusts it up.
Shield and dodges:
Her shield animation would have her hold her staff up to attempt to defend herself and optionally, she could equip the Ward staff when she shields.
Her back roll animation would be based on this dodge animation
https://youtu.be/pqpBe2JhuKw?t=6m4s The uploader does curse shortly after she dodges so here's your warning~
I couldn't find a video showing it but Micaiah also has a dodge animation where she twirls. That could be her forward roll and spot dodge.
Air dodge would be a twirl similar to her spot dodge and forward roll.
Taunts and victory animations:
One of her taunts could be her bow after killing an enemy from Radiant Dawn
https://youtu.be/ig7a_nULdDc?t=6m3s
Another taunt could be Yune flying around her as she twirls before Yune flies back to her
Her last taunt could be based on her twirl animation when she first enters a battle
https://youtu.be/dLoNkLC5FIU?t=46s
Alternatively, she could have a taunt where she sings a galdr
https://youtu.be/lt7Dy-uUhIc?t=5h48m33s would have to be shortened down. Some of these could work as victory animations instead.
One immediate victory animation that comes to mind would be Sothe with Micaiah, standing back to back and looking at the camera.
Another victory animation for Micaiah could be her engulfing herself in blue flames before ending in a calmer pose or a badass one. Could even pull a Toon Link and have two victory animations, both having her engulf in flames but with the different poses. This would reference the cutscene before the final blow to Ashera is dealt.
https://youtu.be/9BI4lYVuWRc?t=18m33s