Ok , I'd like to get a little more serious with the push for Manaphy to S rank. I mean lets be honest, Manaphy is an amazing mon that just terrorizes balance and stall. ITs Tail Glow 3 attacks sets do a number on balance, while tail glow rain dance pretty much 6-0s the majority of stall teams. The Calm Mind rain dance set achieves a similar result to the tail glow set, although it is easier to phase due to not being able to boost as fast, but Manaphy appreciates the boosts especially to its Spdef nonetheless. Now to be fair, thats a bit generic because a lot of mons in this meta excel in breaking balance and some stall teams, such as Char y , Keldeo, Megagross , gengar , Mega Gardevoir, Kyurem B, shadow tag users, Mega Heracross , Lucario, Diggersby, and the list continues if you check the OU role compendium. But Manaphy puts itself in a tier above most of the other wall breakers, as it for one, does not take up a mega slot, and while it lacks immediate power, its power becomes monstrous in 1 turn due to tail glow since base 100 Spa is pretty decent to begin with. In addition to this, it is neutral to Steath rocks, and more importantly, doesnt care about status on some of its best sets. The rain dance set in particular flawlessly gets rid of stall. It uses the premier special wall on stall, eviolite Chansey as setup fodder thanks to being able to rest off seismic tosses and shaking off toxics and thunder waves at the end of each turn thanks to hydration. I'm pretty sure you all , particularly those who have went up against rain dance Manaphy using a stall team are familiar with these calcs.
+6 252 SpA Manaphy Scald vs. 0 HP / 252 SpD Eviolite Chansey in Rain: 333-393 (51.9 - 61.3%) -- guaranteed 2HKO
+6 252 SpA Manaphy Scald vs. 252 HP / 0 SpD Eviolite Chansey in Rain: 417-492 (59.2 - 69.8%) -- guaranteed 2HKO
Now the ability to setup on Chansey is not unique to Manaphy, as contrary Serperior achieves a similar result if carrying taunt. However even if its carrying taunt, Serperior has no way of recovering the damage outside of maybe leftiez and giga drain, and not to mention has far more reliable answers than Manaphy on balance.
Well the two purported best checks to manaphy on balance and stall are mega venusaur and unaware clefable. However they are far from reliable.
252 SpA Manaphy Scald vs. 252 HP / 96+ SpD Clefable in Rain: 148-175 (37.5 - 44.4%) -- 59% chance to 2HKO after Stealth Rock, Leftovers recovery, and burn damage
252 SpA Manaphy Surf vs. 252 HP / 96+ SpD Clefable in Rain: 165-195 (41.8 - 49.4%) -- 24.6% chance to 2HKO after Stealth Rock and Leftovers recovery
As you can see here it only takes Manaphy one scald burn and a roll, which does happen pretty common as you know with scald, for it to not counter Manaphy. This is also compounded by the fact that Clefable can do little back to Manaphy other than perhaps start Calm minding back. In addition to this, some Manaphy can opt to just run surf and the roll to kill Clefable exists after SR.
As for Mega Venusuar, ice beam is usually prefered for Manaphy's grass coverage, and thick fat stands a road block, but even so manaphy can still opt to run psychic:
252 SpA Manaphy Psychic vs. 252 HP / 0 SpD Mega Venusaur: 140-166 (38.4 - 45.6%) -- 12.5% chance to 2HKO after Stealth Rock
+3 252 SpA Manaphy Psychic vs. 252 HP / 0 SpD Mega Venusaur: 350-412 (96.1 - 113.1%) -- guaranteed OHKO after Stealth Rock
So as you can see, manaphy has the tools to cruise by its common answers, nearly has perfect coverage with ice beam scald/surf and energy ball, sits at a decent 100 speed, good bulk, and an anti status ability in hydration. This is a mon that excels over many of our other wall and stall breakers , and is often a first choice for a team needing a wall breaker outside of the mega slot, especially now that Lando I is gone.
Now I've looked at the earlier discussions for Manaphy to go to S rank, and a common argument is the generic "manaphy cant beat offense so shouldnt be S rank" . I mean i have a few problems with this logic. For one , Manaphy is a wall breaker, so its role is breaking defensive teams and the best comparison would be to other things that excel at wall breaking. And even more ironic is that Manaphy is abused by these very same offensive teams that its bad against. Manaphy fits well on those balance teams with Tornadus T and also I've seen it commonly alongside Megagross, another great wall breaker, which takes me to the next step.
Now , Megagross as we know Sits in S rank, and as i noted is a wallbreaking partner in crime. The biggest argument against manaphy going to S rank apparently is that its mediocre 100 benchmark has been too far creeped, making it easy for common HO mons to beat it since it lacks immediate power, and also will struggle to setup a tail glow against faster paced teams since it lacks a speed boosting move. Megagross is a mon with amazing bulk for an offensive mon similar to manaphy, but what gives it an edge over Manaphy is that it sits in a nice 110 speed tier and has, allowing it to speed tie the Latis, Mega Diancie, and Gengar, while also getting the jump on Keldeo and having immediate power to back it up. This makes Megagross undoubtedly better against offense. However, Manaphy excels arguably as well if not better than megagross against balance because its ability to boost quickly against these slower teams very fast in tandem with nearly flawless coverage allows Manaphy to be almost hard to stop and it doesn't care much about getting burned. Megagross is a little more easier to stop because it has to be selective in its 4 move in beating each one of its common hard checks since its dual stab is walled by the same things generally, requiring some more team support to handle the others, and is completely stopped by Mega Scizor. Whereas Manaphy is pretty much only 'Walled' by Mega Venusaur Chansey and Unaware Clef with its standard energy ball ice beam/ hidden power fire /scald coverage, and its rain dance sets pretty much single-handedly blows through most of the other common switch-ins to its 3 attack sets, such as chansey as stated above. Even so, most of the offensive checks to manaphy are the electric types, who manaphy can easily lure in with a wacan berry set, and Manaphy can still check things like talon flame, bulky chomp and staples found in pivot cores such as Scizor Lando- T and Tornadus. Because Manaphy excels in its role so flawlessly in pretty much 6-0 ing stall easier than the rest of the wall breakers , doing a number on balance with a lower opportunity cost than many of the other breakers , being both unpredictable and versatile, it definitely has a lot of positive things going for it. I think these traits should allow it to be placed above some of its A+ brethren, and be placed alongside Mega Metagross in S.