I'd really like to question why Keldeo is S-Rank. I've touched on this before, but I just really don't think it's quite on par with the other S-Ranks. Let's do a little comparison: Deoxys-D: Is virtually impossible to stop from getting hazards up, due to it's great bulk and speed. Very little can actually OHKO it. On top of this, it can beat just about all of it's checks by running the appropriate move, if it wants to. Landorus: It's capable of two entirely different play styles in the form of it's physical, Sand Force sets and its special, Sheer Force sets. Both have an incredible amount of power behind them and have radically different counters. It can even use surprises like Gravity to make it's super powered STAB hit literally everything in the game. Politoed: Drizzle. The power that it provides is incredible and currently dominates the metagame. On top of this, it naturally beats all other weather starters (bar Abomasnow) by virtue of it's typing, making it easy to keep it's own weather up. It also has some decent stats to work with, and can be very Bulky or hard hitting if you want it to. It also has a nice movepool, including some rare moves like Perish Song. Terrakion: It has massive attack power coupled with two extremely powerful STABs that have fantastic coverage together. Very few pokemon can actually boast to resist both, most of which aren't usually seen in OU. It can make a great Revenge Killer, and vicious Wallbreaker, or a deadly sweeper thanks to Swords Dance and Rock Polish. It even can set up Stealth Rocks for the team, while still being incredibly threatening to the opposing team. And now we come to Keldeo: This thing boasts a massive Special Attack stat coupled with STAB Hydro Pump, which hits like a truck, even more so in the omnipresent Rain. It also gets "mixed" coverage thanks to Secret Sword, and like Terrakion can be an effective Revenge Killer, Wall Breaker, or sweeper. Unfortunately, It has very limited coverage, and this is ultimately it's biggest problem. Outside of it's STABs, it's coverage consists of Hidden Power, and Icy Wind. Yep. That's about it. Icy Wind is hardly used anyway due to it being so weak, so that leaves Keldeo with usually just a Hidden Power (Usually Ghost or Ice), along with usually Calm Mind (for Sweeping), or Surf (for Choice sets). This extremely limited coverage is hard on it in OU, where so many pokemon resist or are flat out immune to it's STAB combination. These include Lati@s, Celebi, Dragonite (Well, ALL Dragon/Flying types), Gyarados, Jellicent (who is flat out IMMUNE to both Keldeo's STABs), Tentacruel, Starmie, Toxicroak, Venusaur (and again, ALL Grass/Poison types; this includes Amoonguss, Roserade, etc.) Slowbro/king, and so on. Mind you, these are just the pokemon that resist his STABs; the number of pokemon immune to those individual moves is much greater, which is critical for the Choice sets. So Keldeo has to rely on Hidden Power to get past these. But even then, it can only use one Hidden Power, and the list of counters is so large that one coverage move isn't enough to handle all of them. For example, HP Ice takes care of dangerous Dragons and can hurt Grass types (but keep in mind; without a boost of some kind, Hidden Power is weak), but leaves it walled by those bulky waters. HP Ghost can be used to bypass Psychic and Ghost types, a common type among the Bulky Waters it hates, but then it can't break past Dragons and Grass types. In short, Keldeo no doubt is a great pokemon; Hydro Pump still hits ridiculously hard. But the fact that it has SO MANY COUNTERS, and has pokemon IMMUNE to BOTH it's STABs, I just don't think it's on par with the monsters already present in S-Rank. Feel free to dispute me, though.