Ogma

Insane attack stat, my Ogma currently has S rank support with the Summoner and is level 40+8. With Vantage, Distant Counter and Zanbato+, he can wipe out any horse mage (and any red, green or neutral horse) when under 75% HP with one hit.

With a speed boon, life and death, the speed+3 seal, and the Slaying Edge+ (spd), Ogma reaches a staggering 48 speed, practically doubling everything that isn't just as overinvested as him. An attack boon can work too if that's what you were dealt or think 45 is good enough as is. The idea is to hit something and survive the counter attack with Ogma's natural bulk to put him into desperation 3 range. After that, Ogma would effectively become a Brave Sword+ wielder, capable of hitting twice in a row due to his high speed and desperation passive. Reprisal was chosen as his special just to change things up since he can tank one physical hit fairly well and dish that back out as extra damage, but Moonbow is fine, and more reliable really, since it's also a 2 charge special and synergises well with slaying edge's special charge decrease.

A cheap build for those who want to turn Ogma into a beast. This build is meant to quad units, thus Reciporical Aid is used here. Life and Death is not used here, as it would sacrifice his decent 28 DEF, though he will be absolutely cannibalized by the Reinhardt. Be sure to have someone on your team with a movement assist or the Dance/Sing skill.

(WARNING that my explanation may have run a bit long ((it’s really long)) but go on ahead if you want to see how YOUR Ogma can kill about 147 if the units in this game in one round!)
Now that brash assault is a sacred seal, Ogma can run the set that people put on Lyn: brash assault + desperation. You only need desperation 2 since brash assault 3 procs at half health so save desperation 3 fodder for someone with actual speed (or don’t, wont make a difference really throw him desperation 3 if you have the fodder to do it). Defiant attack also procs at half health and not only does it add more attack than death blow does, Ogma has it at base so you don’t need to throw away klien for death blow 3 (I have no fodder for anything so I can speak that it most definitely is just a lot easier this way.) anyway now the fun stuff: at 50% health, Ogma will be quad attacking 1-range-units, all 4 attacks in succession, with a +7 attack buff. The list of units who will actually survive this onslaught is very short, 21 units in total will live out of the whole roster (as of just after the ayra banner, my math doesn’t include extra skills like fury 3 on units like Xander or ryoma, no buffs like hone Calvary, or sacred seals like def +3 or deflect melee)
that side note might take a bit of the appeal out of this build, but you can use debuffers like Arvis, FemCorrin, or Saizo (personally using saizo with attack smoke) as well as a dancer with wings of mercy to exploit this build even more. These debuffers can easily destroy the defense stats of enemies, Arvis can do it by simply standing in front of the enemy and saizo can exploit the AI bunching enemies together on more open maps and simply debuffing the whole team in a blink (I like saizo so I can be biased, I’m pretty sure none of you also have a 5 Star saizo with summoner support but he can still debuff, you’ll just have a harder time securing kills with him but that’s what Ogma is for)

Long story short, Ogma can become one of the craziest sweepers in the game. Units like Chrom, Cherche, Frederick, or even FlierEmblem Est with a brave Lance can run this same/similar builds with equal to more success, but Ogma has the big advantage of having almost all of the needed skills right at base (he might also be the only one of the above mentioned units I have as a 5star buuuut That was just a random convenience)

So yeah, an extremely powerful build that someone would need prior knowledge of in order to counter (is anybody really running deflect melee other than brave Ike maybe??) Enjoy absolutely crushing anyone who isn’t brave ike, BK, or Arden in the arena as well as having an insane unit to use to destroy those pesky grand hero battle units with like 60 HP, shout out to anyone who actually read through my absurdly long writing

A cheap build that takes advantage of his Brave Sword+

The very famous quadstriking build with an upgraded Squad Ace D 3 seal or Spd seal allows him to hit 40 speed which is enough to quad most of the roster and those who have the speed are unable to survive the first two strikes if they have low defenses.