I'll have to agree Delta 2777 that Deoxys-S is by far the worst suspect left.
Deoxys-S is such a potent threat in the current metagame, because it causes you to fight an uphill battle for the majority of the match, and it does this in a number of ways, the first of which is with entry hazards. While there are other "fast spikers", Deoxys-S is the bulkiest, the only one with Stealth Rock and the most threatening to spinners. Deoxys's bulk is actually quite underrated, as shown by
this set and the fact that it's able to manage getting up entry hazards on Pokemon that "hard counter its offensive sets", such as Specially Defensive Jirachi, which is only doing 30.92% - 36.84% with Iron Head and 22.04% - 25.99% with Body Slam, to the standard 252 HP/252 Spe Support set.
Deoxys-S is not only a great layer of hazards because of its amazing speed tier, but the fact that it has the potential to be threatening to any spinner. It might seem like a good idea to send in your Forretress to Spin away its hazards before taking it down with Gyro Ball, but if you're aware of the many possible attacks this Pokemon can carry, then you're obviously going to hesitate. What if it has Hidden Power Fire/Fire Punch? Then you're Forretress loses a huge chunk of its health, and your best means of beating the Haxorus on your opponent's team is now null and void, the same scenario goes for Tentacruel and Deoxys-S's Psycho Boost, as well as Starmie fearing Thunderbolt. This is purely theoretical, of course, but it's actually a somewhat common scenario, regardless of which Rapid Spinner you have and which threat it counters. Deoxys-S has established itself as a viable user of such a vast array of attacks, that Rapid Spinners feel threatened just switching in, and, through its imposing presence and high Speed, Deoxys-S is able to get Entry Hazards up with ease, making it very hard for a more defensive team to constantly take the brutal attacks of the opponent's remaining sweepers until they can find a time in which their Rapid Spinner can absolve the field of Entry Hazards. The worst part is that there is absolutely no way to tell what Deoxys-S has, other than playing into its hand by trying to scout it while it sets up Hazards/Screens on you and I think Faladran's replay shows this better than words could, so if you send in your Tentacruel, you're essentially taking a stab in the dark; any Pokemon that forces you to do this in order to 'shut them down' is unhealthy for the metagame.
Next up, we have the Screens set, much like the Entry Hazards set, Deoxys-S can get this up relatively easily and while Screens have always been a somewhat large part of the competitive metagame, Deoxys-S isn't set up bait like other Screen Users such as Bronzong, Cresselia, etc and can't be Taunted like the aforementioned Pokemon, unless you're using something like Whimsicott.
The Offensive LO sets are only useful for beating primarily offensive teams, and even then, its attacks aren't that strong and many Pokemon can shake them off, kd24 is spot on in saying that the support sets are the most threatening because they put you at an immediate disadvantage and stopping them from doing their job is no easy task.
I''m going to echo the definition of an Uber Support Pokemon from Katakiri's post, because I believe it characterizes Deoxys-S perfectly and illustrates why it is detrimental to the current metagame.
Support Characteristic
A Pokémon is uber if, in common battle conditions, it can consistently set up a situation in which it makes it substantially easier for other pokemon to sweep.
This sounds quite familiar. Deoxys-S's niche is consistently setting up situations that facilitate sweeping, as illustrated by both of its support sets. You can't deny that Pokemon like Choice Band Haxorus love the 37.5% of residual that the Ferrothorn that was supposed to counter it, just took from the 4 layers of hazards that Deoxys-S set up at the beginning of the battle. To reiterate, Deoxys-S can do this
consistently because it has the ability to pose a threat to the majority of the spinners in the OU Metagame and the fact that it's Screens can't be taunted away, and Brick Break is hardly used for the purpose of smashing screens [not to mention many of the common users of Brick Break such as Scizor are beaten by Deoxys-S if they happen to carry the appropriate attack, in this case it being Fire Punch/Hidden Power Fire].
Finally, while one can argue that Deoxys-S has moveslot syndrome, you can't mess around and scout for its moveset, because it could be setting Spikes all over your field while you do so, unlike the Hidden Power Fire Rotom-W whose waters you can test by sending in a Ferrothorn and then quickly switching it out for something like Latios, because in the process, you aren't put at any kind of disadvantage.
In conclusion, I think Deoxys-S's sheer versatility, threatening presence and unmatched ability to facilitate the sweeping of its team members add up to it a Pokemon that is effectively worthy of a ban from the OU Tier.
