Alfonse

This is probably how I'd build him if... you know.. I actually liked/cared enough to do so. xD

Edit: Oops, meant to switch Quick Riposte, lol.

Honestly, if I ever have to use Alfonse in Arena, I'd probably go all in on his attack and defense through skills and blessings but even then, the best way to do that would be during the Fire season to get the most out of it all.

His refinement makes him a Brick was which means his weapon grants 7 Atk/Def of his Hp if 80% or less. The crazy thing is that he can inherit Brazen Atk/Def to double the effects. This is how I would build Alfonse after the refine:

Folkvangr
Reposition/ Swap
Bonfire/ Ignis/ Draconic Aura
Brazen Atk/Def / SB
Vantage/ QR
Smoke Atk or Def/ Odd Atk Wave
CD

If I ever get around to it.

Folkvangr eff refine
dual rally
Aether
Brazen atk/def
Wrath/Guard/QR or breaker skill (budget)
Atk smoke or drive skill
Close defense or drive seal

Folkvangr eff refine
dual rally
Aether
Brazen atk/def
Wrath/Guard/QR or breaker skill (budget)
Atk smoke or drive skill
Close defense or drive seal

Hi BloodyDawn, several of the frequent responders got together and decided we're going to start encouraging people to put more thought into their play when they ask questions and look for answers with us. I noticed you've asked a lot of "what about this IV" or "how should I build ___" in the past so I'm inviting you have a look through the study I did today. It's a bit different from some of the other ideas that have been offered here, which are as valid as the kinds of ideas I was looking at.
https://fireemblem.gamepress.gg/q-a/ignis-study-building-342631-type-statlines-without-qr

If you would like to discuss further, I suggest showing us a build or part of a build that you might try, and then the community can help you more.

Double Brazen Vantage with Atk Refine

Aside from refining his weapon (with Def), his set of skills will be:
Reposition
Bonfire / Draconic Aura
Brazen Atk/Def 3
Desperation 3
Threaten Def 3
Brash Assault 3

I've been using him with a Brave Sword for some time now. But the build above sounds promising. Even if he will never have any merge potential.

I was also anticipating a unit with a Brazen weapon effect, but I guess he'll be my next focus when I get around to it.