Manaphy
Mew
Ho-oh
Palkia
Dialga
Darkrai
Deoxys-D
Kyogre
Wobbuffet
Lugia
		
		
	 
Kyogre will get one mention, and that is to say that infinite Rain in any team will not only make things like Azumarill and Gyarados unbeatable, it will make Fire types unusable, and other than the X-Act and others have pointed out anything of importance.
 
Out of the whole list, the most stable thing on it is Manaphy, and that's only if it and it alone is unbanned. Manaphy has had tons of threads about it and standard and it's almost unfair not to give it another chance, since all tests made were pre-metagame.
 
Wobbuffet has been tested and tested and tested and can be tested until Nintendo gives Flareon Arceus stats and a movepool to match, but at the end of the day Wobbuffet takes away the best move in the game,(Switching) ties that together with another game-breaking move(Encore) and can set up anything it wants. While the U-Turn/Ghost argument cna be made, Wobb comes in when it wants to, not when it's in danger. In fact, Wobb is even frowned upon in Ubers, so what even gives the thought of standard? 200 Play never wore off on many players.
 
Lugia and Ho-Oh are tied close enough that you can bring them together in lastability. Simply put, they don't die to anything. You thought Hippowdon was hard to bring down, but Lugia is ridiculous, being able to stall far harder hitters. Garchomp and Salamence wold never be the same again from either side of the spectrum. Ho-Oh is a bastard, it only needs to come in once to wreak total havok, even with Stealth Rock. 130 Attack is nothing to joke with, especially with the best Fire attack in the game. Their ability to wall and attack are crazy, don't forget Lugia's Aeroblast or Psycho Boost.
 
Palkia and Dialga, both can be seen from either side of the threat spectrum, and both can change the way games are played. You thought taking Heatran's Specs'd attacks were hard? Try 150 base power over 130 and more diversity. I like that Dialga can wall just about anything without a powerful EarthQuake and that Palkia can be a Bulky Water if need be.
 
Deoxys-D would serve well in OU, actually, walling several threats, but let's not forget that it can actually do something, setting up on weak attackers, and draining PP with Recover and Pressure. The issue is that nothing can really take it out without risking a diverse Deoxys move. It has Attacking potential, amazingly enough, and the bitching would never end. Let's not forget Taunt either.
 
Darkrai is where it gets scary. Jump always mentioned Luna, perhaps the scariest sweeper there is, in comparison to Darkrai, who has all the improvements Jynx wishes it had. If after 2 Calm Minds you 2HKO everything with like 115 base Special Attack, the after 2 with 135, things just die with no chance. Darkrai's Ability alone can make it a threat, the things you team up with it make it nearly unstoppable. Choice Scarf isn't scary when you can put them to sleep or KO them regardless, and Darkrai has the defense to take a hit to KO back. It would be too scary, to deadly, to overpowering to let into OU and not overcentralize.
 
The only things I see not completely overcentralizing the game are Manaphy and Deoxys-D, who can and will change the style of it. I wouldn't mind testing things like Ho-Oh or Manaphy, and personally, even Darkrai, but everything else is just begging for overcentralization and endless bitching.