Originally Posted by Fat Mr.lol
Its low Special Defense stat is its bane. A 252 SpA + Life Orbed Draco Meteor will actually OHKO Groudon. That and Groudon doesn't have reliable Recovery, all it has is Rest. I know Kyogre suffers from similar problems, but since Ubers is more Specially oriented, Groudon actually can't do the same. That and Kyogre has the raw power of Rain boosted Water Spout! Groudon boasts nothing that can come close to that power (well except CB EQ, but I mean there are mons immune to that move... (for the record that's the reason why its so hard for Groudon to run a Choice Scarf set)). Don't get me wrong, Groudon is a great pokemon, its just not enough for S rank.
For the record, Groudon can just Dragon Tail or use Roar on Extremekiller, basically delaying it from sweeping for the rest of the match (its a check).
About recovery,wish support can easily be managed because groudon + [insert pink blob here] walls a lot. While groudon cannot hope to match kyogre's raw power, RP and SD are both much better purely offensive boosting options than CM because they boost a stat by 2 stages.
Defensively, groudon gets stealth rock which is huge and also has the bonus of shutting down excadrill and terrakion as well as some other sand sweepers like landorus rather easily. I still am not sure whether groudon is S-worthy, I'm neutral on this issue as of now but I just wanted to point these things out
I actually fully support Fighting Arceus being moved to A rank. Although not mentioned, Fighting Arceus can actually check Darkrai as it resists Dark Pulse and can swat Darkrai down with Judgment. Its also one of the largest threats to sand teams, capable of KOing Tyranitar and Hippowdon easily, then move on to threaten that Excadrill and Gliscor and Giratina-a on the sand team (if Ho-Oh's on the sand team, I'm not even going to go into how easy it is to setup SR and weaken it so that it falls into range for +1 Ice Beam (that is a lot of prior damage though).
^Pretty much this. Yeah please move fightceus to A. Don't forget it is a good addition to stall as well as offense since it shuts down dark and stell arceus, major threats to stall! Really its only huge flaw is being vulnerable to mewtwo and ho-oh, but it makes up for this by faring better against blissey than other forms. And also, what CM arceus form besides rock isn't
weak to ho-oh?=P