It usually runs Fire, Death and Darkness duos :p
Monowater can deal with it too, and quite well compared to other monos. Ice Shield, Ice Bolts and Chrysaora are all within mono, since you can have a Death mark and still be a mono. If you want a better example, pick Monotime. That's the hardest counter among any elemental opposites. Even Life and Gravity have a chance, but Monotime could only hope to deck out with SoG's, Dials and Turtle Shield. Disallowing Shards, it has no chance whatsoever. Same goes for Monoair without SoFree, except it's at least easier for that to rush and finish off with Shockwaves. Still extremely unlikely.
Regardless, we need more unique in-element cards for balance. I'm extremely happy the Shards are becoming in-element now. It's a step in the right direction.