Since you're running Mordred (with Ambush I hope), Ryu-Oh doesn't seem that appealing? She's -5% Atk, and that's it. Well, back-up debuffs are always good.

The Holy Trinity of Water (Cthulhu-Snow Raphael-SSR Nike) is best complimented by Asherah at the moment, so the question mostly is... are you going to buy one or two Miracle Tickets? Since the x-mas one will probably be available Soon(tm). If so, either complete the Holy Trinity or get SSR Nike and Asherah, maybe?

Notice that there was some discussion about the long term Water teams here.