I have been using my RNG'ed 4th gen Pokemon in the Random Singles so far since I haven't bothered to breed/raise any new 5th gens yet, but its frustrating since everytime I am about to win a battle my opponent quits on me. I have 0 wins on my trainer card because of this, I have yet to have someone take their loss like a man.
I am not really using anything special yet, mainly just throwing out makeshift teams like Nasty Plot Life Orb Raichu/Big Root Giga Drain Venusaur/Super Luck Scope Lens Honckrow. I could care less about winning or losing at this point as I am more interested in seeing what my opponents are brining to the table. Even then, I am still winning at a 50% clip using that team I listed above.
I haven't seen any rain teams yet, but I have seen my fair share of Speed Boost Blazikens that eat me for breakfast, lunch, and dinner. Sleep spamming is very common too, though the last person who thought he could sleep spam me I ended up giving him a taste of his own medicine with my Sleep Powder Venusaur and beating him(he disconnects of course).
It's interesting to say the least right now and I can't wait to actually start taking it seriously and using serious teams on this.