I disagree with both Raikou and Heracross being moved down. In my eyes, when I think of an S-Rank Pokemon, the words "metagame defining" are what come to mind. These two simply fit these words to a tree. Heracross being the king of UU should explain part of it. He is one of the defining forces of UU, and the metagame is basically "Get a Heracross counter, or you lose." Crobat and Cofagrigus have risen to popularity mostly because of Heracross. He is one of the strongest attackers around, and is basically a Pokemon everyone must prepare for. It is a powerful Pokemon, who doesn't come at much cost to use, and much reward exerted. I use Bisharp+Heracross, and Bisharp takes on Heracross counters rather well. Heracross has his counters, but same could be said about shit like Mienshao or Crobat.
Raikou is one of the best, if not THE best special sweeper in UU. He is a high level threat who can easily make work out of teams if given the chance. His SubCM set is beyond amazing, and it has the qualities to get boosting with ease. It is undeniably a top threat; the metagame has come to adapt to it with Pokemon such as Rhyperior, Swampert, and Snorlax. Perior is popular because people NEED a way to stop Raikou, he's that good. If the Pokemon has literally defined the metagame, it's an S-Rank Pokemon.
As for Mr. Cofagrigus, I can argue S-Rank mostly because he's a great and versatile Pokemon. I'm not sure if he defines the meta, but he's S in my eyes mostly because his use is "Low Risk, High Reward". He is the ultimate spinblocker, making him a great fit to keep Blastoise and Claydol from spinning off hazards. Since this is a metagame where Spikes are rather popular, Cofagrigus can easily find himself a spot on teams to keep Blastoise/Claydol from spinning. That's not all. He can counter threats like Heracross and Mienshao with ease, and is pretty good. He has the amazing OTR set, and it can plow through teams relatively easily. This also makes Cofag a good teammate for some legit dangerous threats like Escavalier and Rhyperior. Also, Cofag is capable of being a defensive behemoth. He is a good fit on stall teams, 'cause he walls shit with those high level defenses. Also a great spinblocker. Overall, Cofagrigus is excellent. I'm kinda torn about where he should go, but I'm leaning towards S; I've probably used this thing more than anything simply because he's so damn reliable.
While I'm at it, I might as well nominate Amoonguss for B-Rank. Amoonguss is actually really damn solid in the current UU metagame. It has a decent typing that allows it to endure hits from shit like Kingdra, Mienshao, and Raikou. It also has access to the rare Spore, so it literally eliminates one opponent from the match. DoublePowder is good, after incapacitating an opponent, it can cripple another with Stun Spore. It can wear down with Giga Drain and literally deter setup with Clear Smog. Regenerator is also very cool, so it can switch out and keep its HP intact. Quite surprisingly, it can run a good offensive set. This can deal good damage while healing off LO damage. He has good overall bulk, and enough utility to move up. Despite its flaws in poor Speed, being manhandled by Darmanitan and Azelf, and rival in Roserade, I fell Amoonguss is still solid enough to warrant B-Rank.
<TLCNU> Esca literally is 2HKO'd by Stoutland Fire Fang
Sandslash and Dusknoir for NU!
VM or PM me for a UU / RU rate!