Let's look at some Ubers and see if they can be OU!
Mew:
There is a chance that Mew may be OU, but it has too many moves. It has like 110. It has amazing type coverage, and can BP lots of stat boost, which is the main selling point. In OU I could see Mew as the same rank as, say, Gyarados, but Mew is better than Gyarados at most times. Mew is still a little too powerful for OU, but it may be worth a testing.
Darkrai:
Darkrai is this Pokemon that has average HP and defences, but very good offences. It OHKOs alot of think, even in Ubers, and its ability just adds to that. It is just way too powerful for OU, and it would just be too powerful. Like someone said, it is like every Uber is just knocking on Smogon's door and asking for a testing. Darkrai is good in Ubers, and should stay there.
Arceus:
I don't know why people were asking if the Pokemon GOD could be in OU. I am serious. People are actually think that Arceus is weak enough for OU. It is banned in Ubers. I remember someone saying that there are 1000000 reasons why Arceus is too powerful for UU, and so there are 100000 reasons why Arceus is too powerful OU. Judgement is like a OHKO on anything weak to it. Arceus would destroy OU as we know it!
Ho-Oh:
Ho-Oh has high stats, but it needs better defences It stil can be debated, but its high attack rivals even Snorax's. It probably will need to stay in Ubers for a while before anyone really tries it out, and is for right now we shuld probably forget about it.
Deoxys-D:
Thi thing has to much defence. Blissey can try to stall it, and Toxic is pretty much the end, but for thigs like Infernape, Deoxys-D can really be a threat. It is just like Ho-Oh. It does not deserve a test.
Those were my thoughts about those Pokemon. Vote in the poll!

Mew:
There is a chance that Mew may be OU, but it has too many moves. It has like 110. It has amazing type coverage, and can BP lots of stat boost, which is the main selling point. In OU I could see Mew as the same rank as, say, Gyarados, but Mew is better than Gyarados at most times. Mew is still a little too powerful for OU, but it may be worth a testing.

Darkrai:
Darkrai is this Pokemon that has average HP and defences, but very good offences. It OHKOs alot of think, even in Ubers, and its ability just adds to that. It is just way too powerful for OU, and it would just be too powerful. Like someone said, it is like every Uber is just knocking on Smogon's door and asking for a testing. Darkrai is good in Ubers, and should stay there.

Arceus:
I don't know why people were asking if the Pokemon GOD could be in OU. I am serious. People are actually think that Arceus is weak enough for OU. It is banned in Ubers. I remember someone saying that there are 1000000 reasons why Arceus is too powerful for UU, and so there are 100000 reasons why Arceus is too powerful OU. Judgement is like a OHKO on anything weak to it. Arceus would destroy OU as we know it!

Ho-Oh:
Ho-Oh has high stats, but it needs better defences It stil can be debated, but its high attack rivals even Snorax's. It probably will need to stay in Ubers for a while before anyone really tries it out, and is for right now we shuld probably forget about it.

Deoxys-D:
Thi thing has to much defence. Blissey can try to stall it, and Toxic is pretty much the end, but for thigs like Infernape, Deoxys-D can really be a threat. It is just like Ho-Oh. It does not deserve a test.
Those were my thoughts about those Pokemon. Vote in the poll!