So we all know Anna has a chance to get gold on kill with her luck stat.
Byleth gives magic speed and luck increases. And on a mage class gives the +2 magic range (which works with surge btw or thunder for massive range)
My Sage Anna is one of my fastest units, has insane magic dex and luck. With Byleth giving her all her favorite stats on top of the range is just incredible. I'm almost done my rng maddening run and my God do I love Sage Anna. Skill wise I gave her vantage++. (I didn't give her a second skill yet, thinking speed taker).
With the plus 2 range. I can easily attack a boss still and be in position(assuming my dancer is set) to dance Anna and have her aoe dance everyone. I haven't had this much fun on a magic class in a while.