|With his legendary weapon and high resistance, Arvis has multiple long-range debuffs that can weaken enemy units to improve his own combat capability in addition to supporting his team. He brings the uncommon niche of a being a red mage, and while his speed is rather average, he is perfectly suited to taking out tough and slow green units like Bike or baiting green mages with his large magical bulk.
For his assist skill, Arvis becomes a pseudo-healer by using Ardent Sacrifice. His unique B Skill Recover Ring allows him to generate and share 10 HP every turn to his allies - twice as fast as any other unit with Renewal. This exceptional power to heal therefore makes him an invaluable asset in endurance modes, since a slot in a team does not have to be sacrificed for a dedicated healer. Reciprocal Aid is not recommended, since although it provides a faster heal in some situations, Arvis's low base HP often prevents him from healing teammates fully using this method.
In terms of his A skill, Fury 3 is the best choice. It provides him with a hefty increase to all his stats, which helps to alleviate his mediocre speed and bolster his defenses. In general, Fury's chip damage makes it an undesirable skill for endurance modes, but with Recover Ring Arvis can negate this downside, making Fury an especially powerful skill for him. With Fury, his resistance increases to 36, which ties with Wrys as the highest in the game (assuming neutral res IVs), allowing his debuffs to work against nearly any enemy unit he comes across.
As mentioned above, Arvis's default B skill, Recover Ring, is kept as it is a strictly better version of Renewal 3 that synergizes with both Ardent Sacrifice and Fury.
His C skill, Def Ploy 3 does not benefit his own combat effectiveness but can help soften up targets for physical attackers on his team, fitting his role as support. Alternatively, if it is available, Spd Ploy 3 can also be used, which further remedies his mediocre speed and gives him and the rest of his team the opportunity to double more units.
In terms of his special, Iceberg works well with his high res to nuke an enemy for +18 extra damage when it activates.
His Sacred Seal is flexible to the specific needs and preferences of a team. Deflect Magic 3 is a specific counter to the faster red/green mages like Nino that may kill him when buffed. Otherwise, he can lean to support with any Hone or Spur seal.