Fjorm

She has Replaced my Celica in Baiting mage units or any unit that attacks from a range with the exception of surefire or similar skilled units. This unit who can be obtained for free at the start of the game needs very little help in becoming a strong unit and for her position works Excellently she also leads my water team with Lucina, Kagero and Brave Ike.

This build combines her biggest strength (her great mixed bulk) with the most powerful element of the current meta, Horse Emblems. This way can she lure and kill Reinhardt, Brave Lyn and even Blade Cecilia effectively which gives her a unique place within the current metagame. Of course can she OHKO any Red rider too.
Spd boon is chose to prevent quad attacks from Brave Bow Lyn (who can only get one less point of Spd at the same merge level) and double attack on Cecilia if this one does not use Fury.
Res bane is mandatory to survive Brave Lyn. It is not 100% reliable though, a Lyn with Mulagir and Atk boon might kill her nevertheless. But she will not survive Fjorm's attack too.

Life and Death lets Fjorm get maximum value out of her unique special, while bumping her Atk and Spd up to respectable levels to be able to kill things and prevent doubles. This build lets her tank Reinhardt and even green mages, and kill them in return.

If keeping Fjorm as a ranged counter, Atk+3 seal is recommended to help finish the foe in one attack. As an alternative, she can equip Deflect Magic/Deflect Missile against brave attackers. This does not directly boost her defensive stats and the damage prevented will be added to her attack thanks to Ice Mirror. If opting to utilize Fjorm as a mixed tank, Close Def 3 can be used to help get her bulk back for melee matchups.

This build takes Fjorm's naturally high Resistance and adds the traits of a physical tank to her, transforming her into an infantry Gwendolyn with built-in DC and a free C-skill (since Fjorm doesn't use Armor buffs). Atk/Def Bond and a Close Def seal grant Fjorm 41 Defense and 40 Resistance during close combat, letting her tank physical units and dragons alike then retaliate with a respectable 54 Attack. Quick Riposte is used to work around her mediocre speed, securing kills against fast, squishy units and charging Glacies faster.

While this build focuses on physical combat, Fjorm still possesses high natural Resistance and thus can run Ploy skills effectively; Def Ploy is recommended to boost her damage output against bulky units, but Atk Ploy or even Spd Ploy can be used to increase Fjorm's survivability. Finally, Reposition is chosen both for its ability to rescue her allies and for its synergy with Atk/Def Bond.

This build requires careful positioning to make the most of, but the payoff is immense.

Fury 3 is needed to avoid a ton of doubles from the 36-38 Speed bracket.
With Fury 3, a neutral Fjorm avoids the following doubles:

-Neutral Spe: Elincia, Linde, all Lucina variants, Nino, Tana, Ayra, Lyn, Anna

-Positive Spe: Both Azura variants, Celica, Performing Inigo, Klein, both Olivia variants, Amelia, Summer Corrin, Delthea, Halloween Henry, Innes, Rhajat, Brave Roy, Halloween Sakura, Titania, both Cordelia variants, Eirika, Brave Lyn, all Lucina variants (except the neutral Masked Marth), Nino, Tana

Some of these should be taken with a grain of salt; for instance, Brave Lyn's Speed will probably be boosted through Swift Sparrow 2 or cavalry buffs, and Fjorm can't counter her anyway. But it should be clear that Fury 3 helps her avoid a lot of doubles.