I'd like to bring up an issue that may be blasphemous to a lot of people, but
how the hell is Terrakion S Rank?
I just don't think Terrakion is that good in the current metagame. If you look at Kd24's stats from the last BW tournament, it was used on like one team.
It's certainly not in the same league as Keldeo or Landorus. Is anyone actually scared to see Terrakion in team preview? I'm generally happy to see it, since I know it will be easy to kill with my Keldeo/Breloom/Gengar/Scizor/ScarfRachi/Lati@s/Landorus-T. Compare this to Keldeo, who is resistant to priority and neigh impossible to wall, or Landorus, who literally is checked by about 5 things after a turn of set up, and you begin to see why Terrakion is just plain inferior. Here's its sets:
Choice Band:
Okay, Choice Band is scary. Being able to 2HKO the whole meta can be a bit terrifying. However, it relies on a lot of prediction to decide between CC and Stone Edge. It is easily revenge killed by a good number of mons, and can actually offer set up opportunities to Keldeo or Landorus once it uses Stone Edge or Close Combat respectively.
Choice Scarf:
This is pretty outclassed by Keldeo in my opinion. Even then, it suffers from the same issues as the Choice Band set to an even larger degree, allowing Lati@s and Breloom free turns on the appropriate move, as well as letting half the steel-types in OU set up hazards or launch an attack on Stone Edge.
Lead:
I would say Skarmory is a better lead for HO teams, but I'll grant you Terrakion is a damn good lead. It's lead set isn't enough to make it S Tier though
SubSalac:
Every team has a priority user, so SubSalac is very difficult to pull off, because you generally won't have a Sub up when you have the speed boost and then even an ice shard can kill you. It really likes Magnezone support to get rid of Scizor. This is a threatening set, but I think that Dragonite and Breloom, and even Scizor to an extent, are both better set-up sweepers.
Double Dance, SD Rock Gem, etc: SubSalac is his best sweeping set.
Overall, Terrakion is a great Pokémon. But when I see Politoed in team preview, I brace myself for the onslaught of water. When I see Keldeo in team preview, I'll kill off mons just to give Celebi or Rotom-W a bit of extra health. When I see Landorus, I will sack half my team to make sure it doesn't set up. Terrakion just isn't in the same league as these threats. I would argue that Scizor is much more deserving of S Tier than this guy. There's no way anyone who actually plays OU would ever argue for Terrakion to be banned, and thus I say it belongs in A-Tier.
EDIT: Sorry if this already came up, it wasn't in the past 5 pages and I don't want to read the whole thread...
Reserved for Pokemon who can sweep or wall significant portions of the metagame, but require some support or have some flaws that prevents them from doing this consistently
--i.e weakness to priority and just a bit too slow.