Young Lyon

Weapon: Tome of Grado

Assist: Reposition / flexible

Special: Iceberg / Sol / Glimmer

IVs: +Atk or +Def or +Res / -Spd

Passive A: Sturdy Stance 3 / Triangle Adept / Atk/Res Solo / flexible

Passive B: Null C-Disrupt / Lull Atk/Res / Quick Riposte 

Passive C: Joint Drive Atk / Time’s Pulse / Atk Smoke / flexible

Sacred Seal: Quick Riposte / Mystic Boost / Mirror Stance / flexible

• Staying true to the strengths of his other two forms in FEH, Young Lyon’s Tome of Grado allows him to serve as a good counter to ranged colorless units such as bows and staves. Any time a foe initiates combat or is at 100% health, it debuffs foe Atk and Res by 6 and neutralizes Lyon’s penalties, as well as providing triangle advantage if the foe is a colorless bow, dagger, tome, or staff unit. The rest of the skills in this set are chosen to optimize his performance against those units. 
• A 3-cooldown special such as Iceberg or Sol is ideal for Lyon under most circumstances; his low Speed means he will almost always be naturally doubled by even moderately fast foes, and if he gets a follow-up attack from Quick Riposte, he can activate a Special on his second counterattack. If he is receiving Special cooldown charge from a support unit such as New Years’ Velouria or a unit using Infantry Breath, a 2-cooldown special such as Glimmer could be used instead. 
• The general best boon is +Atk, as Lyon wants to maximize the number of foes he can KO in one counterattack or in two attacks within one combat. +Def is also a great option that gives him more bulk against physical units, since some ranged colorless units such as Ninja Lyn and Legendary Leif can reach extremely high Attack. +Res is an alternate choice that improves his matchup against healers and mages, but Lyon’s high Resistance and Tome of Grado already allow him to beat many of these units without the boon. -Spd is the best bane, since Lyon's speed is terrible and generally not useful.
• Sturdy Stance 3, or another Stance 3 such as Mirror Stance 3, is a highly useful A slot for the combination of stats and slowing enemy Special charge. Lyon’s low Speed means he is highly likely to get doubled by many units, and if he can prevent those units activating a Special on their second attack, he will often take much less damage. The Attack and Defense from Sturdy Stance are arguably the two most useful stats for Lyon, but Mirror Stance 3 is also quite good. Lyon’s base Atk/Res Solo also provides a similar stat buff under different conditions (so long as he is not adjacent to an ally), which are not that difficult to meet in most circumstances, and unlike a Stance 3, it also works on player phase. Triangle Adept is a great budget option that further improves Lyon’s matchups against red and colorless units, allowing him to do more damage and take less so long as those units are not using Cancel Affinity. 
• Lyon has several viable choices of B slot. Null C-Disrupt is arguably the best, as it disables effects such as Dazzling Staff or Firesweep Bow+ that deny counterattacks, allowing Lyon to retaliate and potentially KO those units on enemy phase. Lull Atk/Res provides a debuff of -3 Atk and Res to Lyon’s foes, while also disabling any buffs the foe has in those stats, allowing Lyon to take less damage and do more. Quick Riposte is highly useful for Lyon to guarantee a follow-up on enemy phase, and can be run in either the B slot or the seal. Mystic Boost is another option that gives Lyon some healing and disables Wrathful Staff and adaptive damage. It is generally less useful than Null C-Disrupt, but may be a decent substitute, especially Mystic Boost seal paired with Quick Riposte B as a budget option. 
• The choice of C slot is flexible. Joint Drive Atk provides a boost of 4 attack to Lyon and any allies with 2 spaces, so long as there is at least one ally within 2 spaces of him. Joint Drive Def has not been released at the time of writing this analysis, and it would be a great option for similar reasons. Time’s Pulse reduces Lyon’s Special charge by 1 at the start of player phase, if his cooldown is at maximum. This can be used in combination with a 2-cooldown special such as Glimmer to allow him to activate his special on his first counterattack in his first combat in each enemy phase. Atk Smoke is a decent budget option that debuffs the Attack of any foe within 2 spaces of a foe Lyon fights after combat. 

Weapon: Tome of Grado

Assist: Reposition / flexible

Special: Iceberg / Bonfire / Glimmer

IVs: +Atk / -Spd

Passive A: Mirror Stance 3 / Sturdy Stance 3 / Atk/Res Solo / flexible

Passive B: Special Spiral

Passive C: Time’s Pulse / Joint Drive Atk 

Sacred Seal: Quickened Pulse / Quick Riposte / Atk/Def Solo / flexible

• Lyon can utilize the strengths of Tome of Grado along with Special Spiral to tank hits while retaliating with powerful Specials. When Lyon activates a Special in combat, Special Spiral reduces its charge by 2 after combat. Using a 3-cooldown special such as Iceberg, its charge will be reduced to 1 by Special Spiral, allowing him to get attacked once and immediately activate his Special on the counterattack, so long as his charge is not slowed by an effect such as Guard or Special Fighter. Depending on the combination of skills used, and other factors such as stat boosts from Legendary or Mythic Heroes, it is possible that Lyon’s in-combat Defense will be higher than his Resistance, at which point Bonfire could be used instead of Iceberg. 
• Since the point of this build is to deal as much damage as possible in one counterattack, skills that boost Lyon’s Attack on enemy phase are ideal, along with those that help him activate his special more quickly initially. Mirror Stance 3 boosts Lyon’s Attack and Resistance by 6 while reducing enemy Special charge, effectively boosting Lyon’s Iceberg damage by 9. His base Atk/Res Solo provides the same stat buff without slowing enemy specials, but works on both phases so long as he is not adjacent to an ally, which will be better in some situations. Sturdy Stance 3 is a viable alternative that gives Lyon more Defense, which is useful against some threatening physical units, but only boosts the power of Iceberg by 6 instead of 9.
• Joint Drive Atk is a highly useful C slot to give Lyon more power. Time’s Pulse can be used to give Lyon an initial boost of Special charge and allow him to activate his Special sooner; if combined with Quickened Pulse or an Infantry Pulse from a teammate, he can activate Iceberg on his first counterattack. 
• Quick Riposte seal is useful to allow Lyon to follow-up on enemy phase, which will allow him to activate an Iceberg on his second counterattack provided he gets hit twice and his Special charge is not slowed in any way. If Lyon can obtain two Pulses before his first combat through some means such as Time’s Pulse and a teammate with Infantry Pulse, then a seal that boosts Attack such as Atk/Def Solo or Fierce Stance is useful to push his damage as high as possible. 
• +Atk is the ideal boon, and -Spd the ideal bane, since Lyon’s speed is too low to have an effect on most combats.