Some people say that Deoxys-D is the best at what it does, but what it does is not so great anymore. This is true to an extend. Defog exists, and Latios and Latias sit at 110 Speed and have many opportunities to use it, alongside Excadrill, a fantastic Rapid Spin user. So, this means that when using Deoxys-D you have to provide it the necessary support to make sure that the hazards won't easily be removed and thus your teamslot won't have been wasted. To do this, you need one Defiant user, a spinblocker (even if it dies to Excadrill, being able to spinblock it even once does the trick), and fast, powerful Pokemon that can prevent Defog and Rapid Spiner users from getting rid of the hazards or can punish them hard for getting rid of them. However, Bisharp is one of the best Pokemon to use on hyper offensive teams anyway, due to its strong priority, good sweeping ability, ability to trap threatening Pokemon and pave the way for other Pokemon to sweep, and its ability to check some dangerous threats, such as Clefable, Latios, Latias, and Deoxys-S, so using it on your team is hardly, if ever, a limitation. Defiant Thundurus is a great Pokemon but it's viability stems from the fact that it can punish the use of Defog, so i won't talk about it, because without heavy hazard support, Defiant Thundurus would be replaced by Prankster sets, which are much better outside of punishing Defog users. As for fast and strong Pokemon that can punish the opponent for giving you a free turn, those are exactly the kind of Pokemon that HO teams use, so no limitation here either.
So, basically, the only real limitation when using Deoxys-D is the need to use a Ghost-type if you want to keep your hazards up against Excadrill, a threat that has been on the rise lately. And even though teams with Latios, Latias, Kabutops, or Excadrill can usually find a chance to get rid of hazards or at least threaten to do so in order to get the upper hand of the game, the teams that don't use those Pokemon struggle a lot against Deo-D HO. Even though sand offense, rain offense, and offensive teams in general can deal with the hazards that Deo-D sets up, teams with other, more defensive or balanced anti-hazard means, such as Zapdos, Mega Scizor, Skarmory, and Mandibuzz, can't, and that's where the problems lies. And i am not talking only about stall teams, i am talking about any team that relies on a defensive core to handle offensive threats, all of which usually employ defensive Defog users. Deoxys-D has a huge advantage against any such kind of team, making the game way more offensive and match-up reliant. For those reasons, it's broken.
And that's where Deoxys-S comes in, taking advantage of the offensive metagame to shine with its revenge killing prowess and excellent supporting abilities. Be it support or offense, Deoxys-S does both of those jobs admirably. The first time Deoxys-S was suspected, i voted to keep it in OU, because each individual set wasn't broken imo, and the metagame wasn't mature enough for me to realize Deoxys-S's impact on it. However, now i do. Deoxys-S's combination of dual hazards, Taunt, dual screens, unmatched Speed, and great immediate firepower make it a truly broken Pokemon. It can revenge kill a multitude of Pokemon like no other Pokemon can, and simultaneously set up SR and prevent Defog and Rapid Spin users from getting rid of it with Taunt or its attacking options. It can work as a lead that provides every kind of support you would want on an offensive team, be it Duals Screens, Rain Dance, or dual hazards. And the worst is that it can mix all those roles together, making you struggle to find its moveset, which often comes at the cost of a Pokemon or momentum, momentum which is almost impossible to regain unless you really go out of your way. And that is the biggest problem. Deoxys-S doesn't have a single broken set, but all of them combined together make playing around it a gamble. Whatever Deo-S's purpose on a team is, it will almost always perform it while simultaneously leaving no room to the opponent to regain momentum. Even if Deo-S ends up dying in the process, it will have done its job and it will have put its team to a pretty advantageous position. And when Deo-S can do so many tasks for offensive teams almost flawlessly, you know that something is wrong.
Lastly and obviously, if only Deo-D gets banned, Deo-S will immediately rise to take its position as a dual hazards lead that will be almost as effective. Deoxys-S can fully invest in bulk as it doesn't need any Speed, can outspeed and Taunt every Taunt and hazard user in OU, unlike Deo-D, so it won't have any need for Mental Herb or Magic Coat, freeing up a moveslot or an itemslot. On the itemslot, it can run the Ghost-reducing Berry to be able to set up both layers of hazards against Aegislash. On the moveslot, it can run Reflect, to give it a buffer against physical priority. Or it can use Red Card, similarly with Deoxys-D, in combination with Superpower, making almost sure that it will set up two layers of hazards unless a Scarfer or a priority user comes in, with Superpower taking care of the few Pokemon that can OHKO Deo-S, such as Bisharp and Tyranitar. So, to those who only want Deo-D gone, you can be sure that Deo-S will take its place and force very similar limitations to teambuilding and similar match-up reliance. Deo-S is more or less every bit as effective as Deo-D at a dual hazard setter lead in a Deo-D-less metagame, so if you want Deo-D gone you have to get rid of Deo-S gone too.
