+res -speed zelgius build?

Ouch... I know that feel. I got a -ATK +SPD Hector, among other bad IV pulls. But a fantastic unit with bad IV's is still good. I'd go for an enemy phase build.

Weapon: Alondite. Built in Distant Counter, and it's a high Mt weapon. There's really nothing else out there that's worth using, especially with his low mobility.

Assist: The most common ones for armor units are Swap and Pivot, and I suppose you could use Reposition (though that's probably better used by cavalry, flyer, and infantry units tbh). Smite and Shove might be fun, situational ones, as well.

Special: Black Luna. That thing is insane. 3 turn cooldown, but 80% reduction of enemy's def/res. Though, I wonder if Aether (plus Steady or Warding Breath on slot A) could be viable on him since he'll most likely be getting doubled, thus charging his special faster.

Skill A: Fierce Stance 3, his native skill, is really good, especially as an enemy phase unit. It adds +6 to his counterattack when a foe hits him. The only problem is that there are skills such as Bold Fighter, Desperation, or any of the weapons with the Dazzle effect (foe cannot counterattack) that make him a sitting duck. You could give him Fury 3 to add +3 to atk/def/spd/res, though you'll take 6 chip damage at the end of his turn if he attacks or is attacked. Steady Breath or Warding Breath are also interesting on him to charge up his special for a counter, as well as make him a little more durable while being attacked. With him having 30 speed, getting doubled by most mid-speed and high-speed tier units is a reality, so charging up his special for a retaliatory attack is enticing.

Skill B: The Fighter skills, such as Bold (for player phase attack initiation) or Vengeful (for enemy phase attack receiving) seem to be the popular choices. You could possibly even use Wary Fighter in order to stop him from getting doubled if his HP is above a certain threshold. Wings of Mercy is also a fun option. Vantage is also another possibility. And lastly, Quick Riposte. If he gets initiated upon physically, he's got enough defense to shrug off a lot of green and red units, and he could punish them by hitting twice despite his crippled speed.

Skill C: Now this is where things get really interesting. If you have a unit to sacrifice for it, Armor March is a pretty great skill since every armor unit adjacent to him at the beginning of your turn gains a +1 mobility boost til the end of their turn (including him, though it doesn't give him the boost if he's not next to another armor unit). Unfortunately, that's a rare skill that's locked to 5* units like Amelia and a lot of the seasonal armors. This is where your Goad/Ward/Hone/Fortify Armor skills come in handy. You can stack Goads and Wards, but you can't stack Fortify with Fortify and Hone with Hone. And of course his native Panic Ploy 3 can work for lower HP enemies, though I don't really know how effective this would be on an armor emblem team.

Sacred Seal: Looks like Gamepress really likes to throw Quickened Pulse on him to take advantage of reducing the cooldown count of his special by 1 on the first turn. That, or Close/Distant Def. But he could work with Armor March 1, Speed +3 to fix his bane, or Attack +3 to make him hit harder. And Quick Riposte also works here as a sacred seal.

You've got a lot of options, at least. What other armor units and skills do you have to work with?