What is the best build for Mathilda?

+atk is good and all but tbh I'd prioritize +res or +spd ivs and run dual ploys (spd and def ploy for both survivability and so she could still pack a punch w/out her special) then give her berkut's lance and distant counter so she fight both mages and dragons (distant counter is expensive tho) for other options for A slot you could either have DD, Fury (as a general good over all skill), brazen def/res is good too since we got M-Kana, Mirror stance could be good too to improve her atk and special.