Although it’s been ages since I’ve seen the series, I think I remember the fight between Roy Mustang and Envy from Full Metal Alchemist: Brotherhood to be pretty neat. It was a fun battle with the roles kind of reversed, compared to how things normally go in fighting anime. Roy clearly was the more powerful of the two and Envy just kinda tried to get by with sneaky tricks somehow. Quite engaging. It also helps that I like both of the characters.