Merric

• Preferred IV: +ATK / -HP 
• Weapon: Dark Excalibur
• Assist: Reposition / Reciprocal Aid
• Special: Bonfire / Moonbow
• Passive A: Close Counter / Triangle Adept
• Passive B: Quick Riposte / Vantage / B Tomebreaker
• Passive C: Threaten Res / Flexible
• Sacred Seal: Distant Def / Close Def

Merric's surprisingly sturdy Defense allows him to function as a bait unit for the melee enemy users before striking back hard for a KO. With Close Counter, Merric is capable of retaliating from melee range, which is ideal for him as his Defense stat is high enough to tank physical threats while he wants to avoid the magical threats. Through this, he functions as a very good counter to popular blue units like Effie, Lukas, Ephraim, and Azura, and can kill them easily in the enemy phase.

Bonfire adds a +14 to his damage and Dark Excalibur amplifies that to an impressive +24. When coupled with Quick Riposte, this allows him to counter-KO both Lyn and Reinhardt, as well as lance-wielding units who can double him. Moonbow is an alternative option due to its lower cooldown (lower cooldown = more bonus damage from Dark Excalibur), however, in an Enemy phase situation, Moonbow would proc at the same rate as Bonfire unless Merric was initially attacked by a brave weapon. In these circumstances (such as, if he's attacked by Brave Lyn, Reinhardt, or a brave lance user), then Moonbow is superior- in all other Enemy phase engagements, Bonfire is preferred.

Threaten Res works well with Close Counter, as it allows for Merric to weaken any opponent who approaches him or survives his first counterattack before he attacks them again. Distant Def is preferred as a Seal to help improve his matchups vs blue mages and bow users, particularly Reinhardt and Brave Lyn, however, he's capable of taking them both down without it, it just leaves him with dangerously low HP. To make him better against melee units, Close Def is an attractive option, as it will make him far tankier and increase his Bonfire damage against them.

This set is a generalist set for him and increases his viability in multiple matchups across the board by using his additional Special damage to patch his low Attack and allowing him to utilize Sacred Seals to tank quite a bit of damage for your team.

• Preferred IV: +SPD or +ATK / -HP or -RES
• Weapon: Excalibur (+Eff)
• Assist: Reposition / Reciprocal Aid
• Special: Bonfire / Ignis
• Passive A: Close Counter / Atk/Def Bond / Fury
• Passive B: Quick Riposte / G Tomebreaker
• Passive C: Threaten Res
• Sacred Seals: Close Def / Panic Ploy

As the only non-archer unit who deals bonus damage to fliers, Merric is a great choice against all flier teams, particularly those who think that they're safe because they run a Raven tome Camilla. Since most fliers are melee attackers, Merric still benefits from Close Counter, though he can also make use of Atk/Def Bond and even Fury to patch his Attack, further increase his Defense, and generally boost his capabilities. If both Atk/Def bond and Merric's Excalibur effect is met (there is a mage or staff user within 2 spaces of him) then Merric will effectively gain +10 Attack, +5 Speed, and +5 Defense before any visible buffs. That allows him to do 81 neutral damage to a flier unit in a single hit- not something that a lot of them can recover from! 

Fliers also tend to outspeed him, particularly the meta fliers such as S!Corrin, Cordelia, Tana, and Shanna. Due to this, Merric can run Quick Riposte to attack twice and deal with them effectively. For fliers who run brave sets, such as Hinoka, Cherche, or Cordelia, Merric can prime a Bonfire on his first retaliation, enabling him to counter kill them instantly. As a note, in order to survive a +ATK Death Blow Cherche with Brave Axe, Merric needs to run Close Def as his Seal and cannot be -hp or -def (he survives with 1HP).

To counter Spring Camilla, it's good to run a skill like G Tomebreaker, as Merric's higher Speed will ensure that he can still double her if she's running G Tomebreaker. This ensures that Merric has full reach over both the blues and most of the green units in flier emblem- units like Bridal Sanaki and flying Nino will still threaten him significantly if he's not running G Tomebreaker.

Take care around units such as Palla, Elincia, and Halloween Nowi, though- these three can easily get rid of Merric on initiation. Likewise, Caeda has an impressive Resistance stat and can tank Merric's damage easily.

Close Def is the obvious choice in Sacred Seal if Merric is running Close Counter in his A slot, otherwise he may benefit from Panic Ploy. While his HP isn't the highest at 43, he is still able to Panic Ploy all of flier emblem's mage units (the highest neutral HP being Spring Camilla at 39), therefore preventing flier bladetomes from being a threat to him at all.

• Preferred IV: +SPD or +ATK / -HP or -RES
• Weapon: Gronnraven+
• Assist: Reposition / Reciprocal Aid
• Special: Bonfire
• Passive A: Triangle Adept / Distant Def / Fury / Earth Boost
• Passive B: Quick Riposte / Axebreaker
• Passive C: Threaten Atk / Spur Res / Flexible
• Sacred Seal: Distant Def

Merric is a great choice for running a Raven tome, thanks to his ridiculous HP base. Without Excalibur, he won't be able to counter flier teams, but he gains the ability to tank colorless units like Kagero, Brave Lyn, and Bridal Cordelia much more effectively, all of which could be a threat to him in the arena.

Triangle Adept matches well with a Gronnraven tome as it amplifies the amount of damage dealt while mitigating the amount of damage received. Distant Def and Earth Boost are alternatives to boost his tankiness without losing the ability to damage red and Cancel Affinity. Fury is universally good thanks to the stat boost, but Triangle Adept has more value on Merric.

With Triangle Adept, he kills all blue mages with little difficulty while taking minimum damage from them, including some of the most popular ones like Olwen, Linde and Reinhardt. Most lance users don't stand a chance either as none of them are capable of breaking through his enormous Defense. Only Effie can survive thanks to Wary Fighter.

Quick Riposte allows him to effectively kill units in a single enemy phase, while Axebreaker puts him more in the player phase, allowing him to kill many axe users on initiation, of which the most notable is Hector.