Opposition is one of the most powerful cards in the cube and in any draft format in which it has seen print. No surprise that the cube versions of Opposition decks are very capable and have been kicking around the tier one area since the dawn of cube. It is a bit of a tease having Opposition as a blue card, or at least it used to be when blue had bugger all dorks worth playing. Glare of Subdual felt like it was more in the right place on the colour pie but not tapping lands makes it far far less interesting for cube play. Green was always the pairing colour of choice for Opposition decks as all the good ramp and utility creatures scale so well into the late game with Opposition. Blue can now quite comfortably do a mono Opposition deck but it is more difficult to draft, more damaged when cut and not as all round consistent as the UG version. This list is UGw which is probably the strongest of all should you get the appropriate fixing.
The main joy of UG(x) Opposition decks is that they are so wonderfully easy to draft. I do not mean it is low skill, I mean that the colours are very deep and the kinds of card you are after are broad and well catered for in most cubes. I end up drafting this deck an awful lot as it is very easy to slip into and highly reliable, all you really need is the Opposition, which often doesn't get first picked but is easily first pickable and more often than not the most powerful card in the pack, if not, it is still likely to be the easiest to abuse. So many lowish powered first picks out of nothing better in the pack will end up being ideal in Opposition decks. The white in this list helps to significantly increase the overall power level of the cards in the deck but is not needed at all to make the deck work or plug any gaps. I would never aim to go for a three colour Opposition deck and would only do so if the draft kindly gift wrapped that option, or gave me no other...
Bird of Paradise
Swords to Plowshares
Wall of Blossoms
Wall of Roots
Master of the Wild Hunt
Jace, the Mind Sculptor
Simic Growth Chamber
Once you have your Opposition the only thing that you are really trying to do is cram as many useful creatures into the deck as possible. As the criteria is being a dork, and the cube is full of really good dorks, you can build multiple versions of similarly good Opposition decks that only have Opposition and lands in common. Talking specifically about the choices of dorks I have gone for in this list is not overly helpful in understanding the archetype which is both broader than BG decks, not to mention better. So, as you want lots of guys it is a good idea to get as many of the effects you want to have in your deck in dork form such as Acidic Slime instead of Naturalize and Wall of Roots over Explore / Nature's Lore. In the latter example Wall of Roots is also far superior to Sakura Tribe Elder because you get to ramp and keep a body in play for tapping things later on. More key that the commonly used strategy of having utility dorks is having spells that double up as guys such as living weapon or planeswalkers that make tokens.
Blue and green are the two colours that lack creature removal, Opposition will stop blockers and attackers you don't like but it does little to stop a Grim Lavamancer going to town on your army and you will spend more time with Opposition not in play that you will with it any ways. The counterspells can help in this area but it is not the main, or even a very good reason to include them. You would be far better off with more dedicated removal such as Umezawa's Jitte. Having a third colour as I have done offers the creature kill but it is yet another non-creature card in the deck for the most part and wants to be kept to a minimum. The only half playable single colour removal spells that are also dorks are Flame Tongue Kavu and Shriekmaw. Bounce and control magic effects I find tend to work out pretty well when no third colour is an option. Bounce effects are easy to find on decent creatures and work very well in your deck. Mana critters combined with bounce dorks give you a huge tempo edge, combined with counter magic they offer a more reliable way of dealing with pesky dorks and combined with Opposition they can stop bounced things ever coming back to play. The list I have given is very much on the light side of ways to deal with dorks and is more focused on card advantage and creature power to compensate for this lacking.
The final weakness of the archetype is that it can run out of gas very easily. In a top deck situation you are often in real trouble as so many of your cards are do nothing Elves and you have few serious threat cards. This list is very very high on card draw effects with Jace, Skullclamp and Consecrated Sphinx, all serious card draw engines. You do not need to go this all out on it but some is certainly needed unless you end up only playing really high power cards, which in turn means you will lose to any vaguely quick deck.
I feel I need to rise to my own challenge and make a viable list that uses very few of the same cards to illustrate the depth of the archetype.
Birds of Paradise
Squee, Goblin Nabob
Kira, Great Glass-Spinner
Man O' War
Sower of Temptation
Glen Eldandra Archmage
Meluko, the Clouded Mirror
Force of Will
16 Lands including a Treetop Village
Ok, so not quite no overlap, Birds of Paradise and Eternal Witness are too juicy, I very nearly put some two mana walls in the second list as well!