Eh, the Yin-Yang orbs aren't really too bad, to be honest. At that point, you should definitely have Diamond Blizzard Lv. 1, so you can do nice damage to them pretty easily given the relatively low cost and Cirno's nice MP pool.
Or, y'know, just Wriggle em. Seriously, Wriggle's insanely good there. sure, she's costly to Call, but when you do, stuff dies. Like ~400 damage to everything AND Poison... Those orbs are dead. Plus, free Orb Lv. 2 scrolls. =)
Their only "strong" attack is that draining attack they occasionally use, IMO. Even then, it's rare enough to not be a big problem. Kinda sucks how useless Meiling is against em though due to their ridiculous defense value.
And, as you said, Patchy's good against em. But Patchy's good against EVERYTHING to some degree, so that's kinda expected. Loving her super-low cost all-targetting spell, I am. (6 MP out of a pool of over a hundred? Yeah, she can do that as long as she likes.)