Lyon

Lyon's weapon refine makes him a surprisingly good unit, as it gives him something that he needs in almost every build he gets, which is quick riposte, and a lull atk/res effect that will help with his bulk (being an old unit means that he will need a lot of help on that department), since he doesn't have the same stats as some of his other iterations, but that quick riposte might give him some advantage over his fallen alt (Though Blood Tome is definitely more powerful for a defensive playstyle, as it gives damage reduction).

The build is centered around him getting to debuff the enemy on combat to overcome the opponent with every attack. Due to that, Fatal Smoke is key to avoid that the enemy recovers with Aether, sol, or basically any healing. In that sense, he is similar to Duo Lif, a dangerous unit that many people use as a fatal smoke user (You can also go for a more debuff oriented strategy with Atk/Res threat or Atk/Res menace which would make him incredibly dangerous, as the closest unit wouldn't even dream of hurting Lyon, as it would give -6 to atk and res for the opponent, and +6 to atk and res for Lyon, but the hero builder still hasn't implemented the Atk/Res menace, so, for the time being, the build goes well like this). Although, Lyon is able to use double lull skills to effectively cripple the enemy's atk and res, making him a dangerous unit. As seal, we get Fort Def/Res 2, as Lyon's defense is workable, but you can see that he isn't as bulky as newer units (this might reduce a bit the damage output, but in return, it allows for better endurance).

For the Special, it will be centered around healing, Sol allows for more consistent healing, but he could run Aether to ensure a KO (though you will have to take into account his health thresholds, as under 75% you lose quick riposte, and under 50% you lose the built-in lull atk/res).

And for the A skill, close foil is a good skill, since the res department seems to be taken care of, we might have to worry about the melee units that might want to kill him. As such, we'll run Close Foil to mitigate heavy melee hitters attacks (you can also run close counter if you don't have close foil). That plus the lulls should be enough to deal with dangerous threats

And for the assist, it's really not that important, but in case you like Lyon (he is one of my favourite units, and I want him to be somewhat reliable, so, I give him a good one, but on budget, this is already quite expensive without the rally) and want to give him a good assist, any rally will be of help for the entire team (depends on the team, you might want to run atk/res, or maybe atk/def. )

Cheap and effective build for Lyon that allows him to work as a hard counter to several commonly used AR and Arena units.
I prefer to use Quick Riposre in Seal Slot rather than B since Sword Breaker seal doesnt excist yet.
Note: After Sophie got his Weapon Refine and Resplendit attire, she can use the same kit more effectively than Lyon. She can also get a +Atk/-Spd IVs to further improve the build.

Newly Updated Lyon at +7 and has summoner support. Ultimate anti-horse unit. If you don't want to give him Close Counter, give him Mirror stance to survive chill res Reinhardt. He screws over Veronica, and Firesweep Lyn,and survives just about all horse mages depending on support. Really fun to use.

Kills all grey units (except innes) and sword units if he can attack first. Glimmer is quicker than iceberg and will confirm ORKOs on many units that Lyon comes close to killing in one shot/round, but just doesn't make it. Pairs well with green units who can help take out blue units.

The recommended Raven tome build for Lyon, that is able to tackle most colorless, green and red sword units easily. Currently he is the focus of my merge project, so his stats will change soon enough.

Naglfar is Lyon's own Raven tome that is a lot stronger than a regular Raven tome, and aids him in being able to take on colorless units like Brave Lyn and Halloween Jakob. Triangle Adept increases his power not only against colorless units, but also green units as well.

Swordbreaker allows Lyon to double Red sword units while his HP is above 50%, and allows Lyon to have an advantage against three different unit types, more than most other units in the game cannot have.

Atk Smoke allows Lyon to reduce the attack of any units in a 2-space vicinity of him by -7, allowing him to be slightly more bulky should he be in range of a physical unit.

Quick Riposte allows Lyon to attack twice on an enemy unit while his HP is above 70%, to make up for his bad Speed stat.