Need some advice on a builds !!

His C skill and seal are good if he’s near other units when he attacks, otherwise you can easily swap those out since he’s going to flier emblem. I’d say the way you have him now is pretty good, but DC plus QR seal and vantage sounds too good to pass up (although I’m sure they will make Vantage a seal before too long).

It’s your call. But at the minimum, swap out your breath of life seal and c skill for a flier buff such as goad or fortify fliers.

EDIT: if running QR, make sure he has a buffed up res due to his subpar value. Daggers will die on initiation, and only a Brave Bow user could make his DC seem useless. Even then, a DC plus vantage would most likely take anyone not named Brave Lyn down before you had to worry about getting hit.

With the current meta game, I feel like putting DC on him would be a waste. He has low res where green mages and Reinhardt are meta, and since he's a flier brave bow users (Bride Cordi and B!Lyn) will shit on him as well. He'd probably get 1RKO before even getting into his vantage range. I think leaving him on your flier emblem team is fine though. Here's a few popular Arena units that I was talking about. All of them are vanilla, unbuffed, aside from Nino w/ Fury and the archers having Brave Bow+ vs. the suggested Valter build.