Water Walking

[Undyne]

I agree that Water Walking should be a move if you can use it in any way that gives you a distinct advantage - as in fighting scenarios, a base assault or what have you.
In Arthuria's case, if she can walk on the lake water to get her sword - and really, the only alternative would be swimming, which would not have any major difference - but outside of that single occasion she needs to swim around to cross bodies of water, I personally wouldn't mind.