Ok I just need to sort out everything since these ranking threads (the discussion, not the actual rankings, PK's doing an astounding job). First of all I was looking for a quote that Lavos said before when it came to Breloom's potential promotion to S-Rank but I couldn't find it. It goes something along the lines of "We are going back to Deo-D again, 4MSS isn't a good thing" That sums up what people are saying about Terrakion.
First off Tangrowth and Slowbro can shove off X-Scissors unless its CB (even then I think it doesn't get 2HKOed after Lefties, I'll put all the calcs in the end) as it barely does more damage than a non-SE Stone Edge. Terrakion is a LOT worse than Keldeo now as it basically has a more severe case of what ciaranroy said when it comes to being too easy to counter. There are multiple occasions in teambuilding that you can easily just get ~3 checks to Terrakion without even taking it into too much consideration. Let's say I have a team around KelTarLando (probably the 2nd most common teams to see in comp. play). Won't you look at that, I already have a (probably) scarfer to check CB Terrakion and speed tie with opp scarf terrakion, a lure for CC so Lando gets free setup. To continue to elaborate on that, most of these teams will probably pack a Celebi, Jirachi, or Landorus-Therian (It's not even that uncommon to pack all three). If Jirachi is scarfed it revenges CB Terrakion, Celebi can take switch into CCs and forces Terrakion to rely on SE's accuracy or odd prediction with X-Scissor, which subsequently leads to Landorus setup, unless it has X-Scissor without a choice set, which is dumb. and lastly Landorus-Therian is there as easily the most viable Terrakion check. Sand Offense teams even tend to carry Scizor or Rotom-W, who even though they don't really check Terrakion (scizor does), is something Terrakion doesn't appreciate. Rain Offense isn't really as kind to it as Tentacruel can stop some CC's while Ferrothorn stops the SE's. Even then they are revenged by Scarf Keldeo given proper speed tie or Politoed at Full HP. Scarf Terrakion doesn't really have enough power to muscle through FerroCruel anyway. The idea that Terrakion isn't really threatening much team matchup-wise (an essence of BW2 OU) also shows in the Smogon Tour usage stats by kd24.
1.] Jirachi: --------- 44.74%
2.] Landorus-T: ---- 31.58%
3.] Politoed: -------- 28.95%
4.] Keldeo: --------- 27.63%
5.] Scizor: ---------- 27.63%
6.] Rotom-W: ------- 26.32%
7.] Starmie: --------- 22.37%
8.] Tyranitar: ------- 22.37%
9.] Landorus: ------- 19.74%
10.] Garchomp: ------ 19.74%
11.] Thundurus-T: --- 17.11%
12.] Latias: ---------- 17.11%
13.] Skarmory: ------- 17.11%
14.] Forretress: ----- 14.47%
15.] Kyurem-B: ------ 14.47%
16.] Ferrothorn: ------ 15.79%
17] Latios: ---------- 14.47%
18.] Heatran: -------- 13.16%
19.] Gengar: ---------- 13.16%
20.] Dragonite: ------- 11.84%
21.] Celebi: ---------- 11.84%
22.] Ninetales: ------- 10.53%
23.] Breloom: -------- 10.53%
24.] Hippowdon: ----- 10.53%
25.] Alakazam: ------- 10.53%
26.] Amoongus: ------ 9.21%
27.] Venusaur: ------- 9.21%
28.] Terrakion: ------- 9.21%
That actually makes me remember that Latios also fares well vs most Terrakion
Yeah so as we can see, Terrakion really dropped here in usage due to having not really performing well against prevalent styles in the competitive scene. I also just wanna briefly go over sun, Dugtrio TRAPS it while Venu/Sawsbuck/Lilligant revenges it so that's not a great matchup as that's 50% of their offense (I also wanna point out that Scarf Gothitelle revenge kills it, but I'm not sure if I'm the only one who uses that in Sun).
Now let's move on and see why Keldeo is so good. I think the magic rule that makes Keldeo really solid in this metagame is "what doesn't counter Keldeo is checked by Keldeo". I think that applies for 80% of the metagame now. Let's use these stats just as a quick example. The Keldeo checks we see here are Celebi, Latios, Latias, Amoongus, Chlorophyll sweepers, and Starmie. That I think sums up every single bit of what I see that truly counters Keldeo (Rotom-W and Alakazam are shaky at best). So let's see what that leaves by descending down on the usage and see if Keldeo checks them.
[BOX]
1.]
Jirachi: --------- 44.74% (one of the few exceptions to my rule)
2.]
Landorus-T: ---- 31.58% (checked by Keldeo)
3.]
Politoed: -------- 28.95% (Politoed's existence actually HELPS Keldeo, Scarf Keldeo also revenge kills a majority of rain mons.)
4.]
Keldeo: --------- 27.63% (mirror)
5.]
Scizor: ---------- 27.63% (checked by Keldeo)
6.]
Rotom-W: ------- 26.32% (Shaky check)
7.]
Starmie: --------- 22.37%
8.]
Tyranitar: ------- 22.37% (Checked by keldeo)
9.]
Landorus: ------- 19.74% (Checked by keldeo before boost, you can't really say Lando beats Keldeo well either)
10.]
Garchomp: ------ 19.74% (Checked by keldeo)
11.]
Thundurus-T: --- 17.11% (Checked by keldeo)
12.]
Latias: ---------- 17.11%
13.]
Skarmory: ------- 17.11% (an odd exception, Brave Bird nails Keldeo on the switchin and such but Keldeo can easily muscle through skarm)
14.]
Forretress: ----- 14.47% (Checked by keldeo)
15.]
Kyurem-B: ------ 14.47% (Checked by keldeo)
16.]
Ferrothorn: ------ 15.79% (Checked by keldeo after a bit of prior damage)
17]
Latios: ---------- 14.47%
18.]
Heatran: -------- 13.16% (Checked by keldeo)
19.]
Gengar: ---------- 13.16% (Revenged killed by most Keldeo)
20.]
Dragonite: ------- 11.84% (Checked by keldeo)
21.]
Celebi: ---------- 11.84%
22.]
Ninetales: ------- 10.53% (Checked by keldeo sorta)
23.]
Breloom: -------- 10.53% (Checked by keldeo)
24.]
Hippowdon: ----- 10.53% (Checked by keldeo)
25.]
Alakazam: ------- 10.53%
26.]
Amoongus: ------ 9.21%
27.]
Venusaur: ------- 9.21%
28.]
Terrakion: ------- 9.21% (Checked by keldeo)
[/BOX]
From there we can see that Keldeo revenge kills 60.7% of relevant threats in the metagame with its SE coverage and speed, which is a great feat to have and is definitely S-Rank deserving. If that isn't enough, I'm just going to bring out a point that has been exhausted many times, which is the point of KelTar and other cores that can work with Keldeo. The thing about Keldeo's checks is that most of them are very exploitable, first of all the ones up in the tier list have trouble with Pursuit, which leads to KelTar being great, and there are a few other things that work here such as partnering decently with Thundurus-T+Scizor combo in rain teams. Another thing to look at is Keldeos amazing synergy with Signal Beam/Tbolt/Psyshock Gothitelle, who can trap a majority of Keldeo's checks. This shows that even the Pokemon that check Keldeo are easily exploitable with a few exceptions, which were primarily built JUST to beat Keldeo. To me, that definitely warrants an S-Rank.
I think that justified Keldeo>Terrakion rather well, and if anything just showed why Terrakion should drop rather than Keldeo. Damn, that felt like one of those debate challenges in serenesforest