I'm a bit unfamiliar with the UU metagame, so I ask this blindly.
Mew was uber in 4th gen. What happened (metagame-wise or pokemon-wise) to cause it to drop to UU?
To really understand this you have to understand tiering politics a little bit. Before the 5th generation, we would always carry over the last gen's ban list and just use that as a starting point. This wasn't the smartest decision, since mechanics changed so dramatically. Essentially, Mew was grandfathered in. In Generation 4, Mew was never tested, so it was Uber.
In Gen 5, we started with a much shorter ban list and tested a lot of threats. This is why the Lati twins, Deoxys-D, etc. are OU. However, Mew did not find much of a place in OU. Between power creep (Pokemon have been steadily increasing in offensive power every generation since Gen 2) and a metagame dominated by Pokemon that eat Psychics for lunch, and Mew didn't have much of a chance. He was a bit of a jack of all trades, but not exceptional at anything valuable in the metagame that couldn't be better done by another Pokemon.
So he fell to UU, where the consensus is that Mew is quite good, but not exactly broken.
Why was Wobbuffet banned? And what is the difference between wobb and wynaut?
Essentially, acceptable defenses combined with Encore and Shadow Tag enabled Wobbufett to make any Pokemon into set up fodder. Simply Encore, and then if they attacked, you can KO them with the appropriate move. If they didn't, you switch out to another Pokemon and are guaranteed a turn of set up.
Wynaut can do something similar, but he has a much harder time doing so due to the lower defenses and Speed, even after Eviolite. Thus he can set up on fewer Pokemon and thus hasn't proven to be broken yet.
I'm currently using a Honchkrow with the following set:
Big Daddy (Honchkrow) (M) @ Life Orb
Trait: Moxie
EVs: 4 HP / 252 Atk / 252 Spd
Adamant Nature
- Pursuit
- Sucker Punch
- Brave Bird
- Superpower
I love this set so far, as it's good at Pursuit-killing Pokemon weak to Honchkrow if they decide to switch out into a Honchkrow check with a better chance, but I've found that, without Roost, this Honchkrow wears itself out very quickly, especially if I couldn't get SR off the field.
Would BlackGlasses be an acceptable alternative? Or would the 10% damage drop from Life Orb cause me to lose out on too many OHKO's and 2HKO's?
http://honko.byethost8.com/manly_calc.html will help you make this decision, particularly the "one versus all" calculator that lets you get a good idea what Honchkrow does to EVERY Pokemon in the metagame.