Gordin

Brave archer build, pretty straightforward. Chose bonfire to maximize his second turn. Bowbreaker for a reliable lyn check. hone spd due to the team i put him in, they are in need of a speed buffer so he's it!

an alternative build I might run down the line is to get moonbow and quickened pulse instead. perhaps that setup might also swap death blow for attack+3 to have better enemy phase.

A very specific defensive build aiming to check fully merged Brave Lyns and Reinhardts using an unmerged Gordin. Gordin is one of the few heroes who can safely handle multiple variants of Brave Lyn. Gordin's RES is also low enough to not take a lot of extra damage from Moonbow allowing him to survive in certain situations. While he is able to check one of the two heroes, he cannot safely handle both on the same enemy phase.

The following is assumed of the enemies

+10 merged
+ATK
Death Blow 3
Moonbow
Hone Cavalry

Against Brave Lyn, Gordin will have 44 defense on the enemy phase giving him enough bulk to take a Moonbow from a fully merged Brave Lyn. He can then retaliate with Glimmer allowing to kill her in one shot. Bowbreaker allows Gordin to defeat Brave Lyns with Mulagir.

Gordin paired with Deflect Magic is also enough to take fully decked hit from Reinhardt as well. He won't be able to kill Reinhardt however until the next player phase. Despite Gordin's SPD bane, he shouldn't be able to get quadded unless Reinhardt has several goad buffs along with hone. Gordin will still fall if Reinhardt opts to run Glimmer instead however.

Outside of Brave Lyn and Reinhardt, this build is very apt at countering bow and dagger users. He will still fall to mages fairly easily since deflect magic does not kick in. He also won't able contribute much outside of chip damage against everyone else due to a very weak player phase. Despite this he can finds a very useful niche able to defeat two of Arena's most common in their most optimal builds without having to be a Green Raventome user.

This Gordin has the niche of completely nullifying any damage from two range physical units. With variations of this build, all archers who aren't equipped with bowbreaker will easily let Gordin live on above half health, including the infamous Horse buffed Brave Lyn. This Gordin will also be able to live some weaker mages and non-wrathful staff clerics, but for the most part he will be avoiding magic users. I will go into depth about some variations of this set.

The Guard bow is necessary so it must stay.

For the A skill, Distant Defense is best because it gives the highest buff to defense for this set without ruining his attack any more. Steady Breath or stance may be used as well but they are even harder to come by and make any mages he could survive kill him. For a budget build use defense +3 over fortress defense to avoid hurting his bad attack.

For a B skill Quick Riposte is nearly always the best option, he needs to double most targets to activate bonfire or another special if using steady breath. Bowbreaker may be used for a budget since he will mainly be killing archers, but be aware he will not activate bonfire this way.

C skill is very flexible but threaten attack will increase the amount of mages he can potentially live and make Bows do even less damage.

For the seal I chose attack +3 since giving defense gives +4 in the refinery as giving attack is less than that, but it is still an option if your . Running distant defense 3 is arguably but is better off for units who are dealing with mages as well. You generally don't want to put all of the effort into either attack or defense as his attack is lacking and he requires additional defense to make his tanking potential as high as possible.

Gordin has 3 viable specials:
Bonfire lets him activate a special every time he is in combat meaning even bulkier archers or daggers will be killed
Ignis lets him drop a giant nuke on the turn after combat with an archer or may be used if relying on steady breath instead of DD
Aether is for keeping his health up for QR but is not reccomended due to it's rarity and generally being useless outside of Steady Breath builds.

This build works like a tankier Klein and is a very good counter on enemy phase, hence the bow breaker. The defense boon could be swapped with an attack bonn to secure more damage on other non-distant counter units. Swap can also replace reposition to take advantage of his somewhat armor like defense, and qp can replace ignis for more consistent procs.

With +def and -spd Gordin can use Brash Assault to deal heavy damage to enemy dagger and bow users with lower attack stats. Gordin will need a team mate who can deal with mages with his low res therefore rally resistance helps him assist his teammates in dealing with enemy mages.
(Not tested in game)