I reached the rating requirements a few days too late playing a heavily flawed team based off the team I played during the Cresselia / Porygonz metagame ... the experience really showed me why I stopped playing as much: just too much pressure, and making a good team takes too much time. I want to play, except I know my team has flaws that aren't easily fixed (sigh). At the same time, I don't want to play, because I'm afraid of losing (even deeper sigh).
Anyway ...
Umbreon can be forced out by phazing. I've noticed that some teams have stopped running phazers. Weird, because I find myself relying on Roar / Whirlwind to get rid of Pokemon behind Substitutes a fair bit.
I've been using Sunnybeam Moltres a bit. It's a great Pokemon, capable of removing Rain / Sandstorm / Hail (beat some teams like that - they see I'm not running Rain / Sun and so assume I have no weather, letting Snover die, after which Sunnybeam Moltres sweeps their team easily). Aside from the persistent 50% weakness to Stealth Rock, there's only one problem. Fire + Grass is handily walled by opposing fire types. Pokemon with Flash Fire are especially bad. You are forced to use Solarbeam, which in turn boosts their fire attacks to use on you. I'd imagine the same problem exists for Sunny Day Ninetales. Switching loses you your Nasty Plot boosts, while you'd have set up the sun for their Fire sweepers, and you might've lost 25% HP to Stealth Rock without recovery.
On the other hand, since Fire is a bad defensive type there usually aren't defensive Fire Pokemon around. And since Fire is weak to Stealth Rock, SR can really really really aid a sweep here.