I'm going to ask to bring Serperior up to B rank. Serperior, simply put, is a train that has no brakes. Serperior's way of simply firing off a nuke of an attack and getting +2 on it without having to take a turn to set up makes it an incredibly hard Pokemon to stop. +2 Leaf Storm or Dragon Pulse easily muscles through many of Serperior's checks (bar heatran) easily after Stealth Rock, and only a select amount of Pokemon can *actually* reliably beat Serperior by either being faster, having a type advantage (very unreliable because even shit like Mega Altaria take about 55-70% damage at +2 which is berserk), or having a Speed advantage, such as Pidgeot/Tornadus. Not even Stall can handle Serperior, actually. Chansey is eventually just 2HKOed, Unaware Clefable is 2HKOed fullstop, Cresselia is 2HKOed, just everything dies.
+2 252 SpA Life Orb Serperior Leaf Storm vs. 4 HP / 252 SpD Eviolite Chansey: 196-231 (30.5 - 35.9%) -- guaranteed 3HKO after Stealth Rock
+4 252 SpA Life Orb Serperior Leaf Storm vs. 4 HP / 252 SpD Eviolite Chansey: 294-347 (45.7 - 54%) -- guaranteed 2HKO after Stealth Rock
+6 252 SpA Life Orb Serperior Leaf Storm vs. 4 HP / 252 SpD Eviolite Chansey: 390-460 (60.7 - 71.6%) -- guaranteed 2HKO after Stealth Rock
And then obviously you just regain your health with Giga Drain after the +6 hit.
To reiterate on what I mean when I say about "resists are easily muscled through":
+2 252 SpA Life Orb Serperior Leaf Storm vs. 0 HP / 0 SpD Thundurus: 230-272 (76.9 - 90.9%) -- guaranteed OHKO after Stealth Rock
+2 252 SpA Life Orb Serperior Leaf Storm vs. 4 HP / 0 SpD Bisharp: 256-302 (94.1 - 111%) -- 68.8% chance to OHKO
+2 252 SpA Life Orb Serperior Dragon Pulse vs. 0 HP / 4 SpD Latios: 309-364 (103.3 - 121.7%) -- guaranteed OHKO
+2 252 SpA Life Orb Serperior Leaf Storm vs. 252 HP / 4 SpD Klefki: 214-252 (67.2 - 79.2%) -- guaranteed 2HKO after Stealth Rock (granted you'll be t-waved but yeah)
+2 252 SpA Life Orb Serperior Leaf Storm vs. 248 HP / 108 SpD Mandibuzz: 178-211 (42 - 49.8%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
So obviously at +2 (which is so fucking easy to get) Serperior just is anal to deal with. To top this all off, base 113 Speed means that it outspeeds the coveted 110 Speed tier, and outspeeds just up to Thundurus, which is actually just absurd. So, honestly, we're dealing with a monster that takes no turns to do ridiculous damage and outspeeds half the metagame. Move to B
+2 252 SpA Life Orb Serperior Leaf Storm vs. 4 HP / 252 SpD Eviolite Chansey: 196-231 (30.5 - 35.9%) -- guaranteed 3HKO after Stealth Rock
+4 252 SpA Life Orb Serperior Leaf Storm vs. 4 HP / 252 SpD Eviolite Chansey: 294-347 (45.7 - 54%) -- guaranteed 2HKO after Stealth Rock
+6 252 SpA Life Orb Serperior Leaf Storm vs. 4 HP / 252 SpD Eviolite Chansey: 390-460 (60.7 - 71.6%) -- guaranteed 2HKO after Stealth Rock
And then obviously you just regain your health with Giga Drain after the +6 hit.
To reiterate on what I mean when I say about "resists are easily muscled through":
+2 252 SpA Life Orb Serperior Leaf Storm vs. 0 HP / 0 SpD Thundurus: 230-272 (76.9 - 90.9%) -- guaranteed OHKO after Stealth Rock
+2 252 SpA Life Orb Serperior Leaf Storm vs. 4 HP / 0 SpD Bisharp: 256-302 (94.1 - 111%) -- 68.8% chance to OHKO
+2 252 SpA Life Orb Serperior Dragon Pulse vs. 0 HP / 4 SpD Latios: 309-364 (103.3 - 121.7%) -- guaranteed OHKO
+2 252 SpA Life Orb Serperior Leaf Storm vs. 252 HP / 4 SpD Klefki: 214-252 (67.2 - 79.2%) -- guaranteed 2HKO after Stealth Rock (granted you'll be t-waved but yeah)
+2 252 SpA Life Orb Serperior Leaf Storm vs. 248 HP / 108 SpD Mandibuzz: 178-211 (42 - 49.8%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
So obviously at +2 (which is so fucking easy to get) Serperior just is anal to deal with. To top this all off, base 113 Speed means that it outspeeds the coveted 110 Speed tier, and outspeeds just up to Thundurus, which is actually just absurd. So, honestly, we're dealing with a monster that takes no turns to do ridiculous damage and outspeeds half the metagame. Move to B