Hello all! I got like a week break of arguing and I'm right back and ready to kick this in to gear again! Don't expect me to respond to anything/be vigilant of points already made since this thread is going to move like a Japanese bullet train. I also type like a six year-old.
So first off, I am going to be pro-ban for the duration of this thread. The reasons shall be thoroughly (I would hope) justified and explained below.
Let's talk about the stats.
On the defensive side, we have a 105/100/100, normal typing. This grants, as you all know, one weakness (fight) and one immunity (ghost) as well as being resisted by rock and steel and cannot touch ghost. The trade offs is it doesn't resist any types, but as a sweeper this is fine. We're not talking about a wall. A sweeper with the ability to be threatened by only one type for SE damage (And in that, one priority type) is a good sweeper in deed.
As I generally care more about defenses, let's talk about other pokemon in that same defensive tier.
Celebi, Jirachi, Ferrothorn and Heatran all are really solid defensive pokemon. In fact, in the terms of walls/tanks, you can't ask for too much more. But Celebi and Jirachi already have less bulk. Heatran and ferro have different styles, so let's see how they stack up:
252 Atk Garchomp Earthquake vs. 252 HP / 252 Def Ferrothorn: 108-127 (30.6 - 36%) -- 48.2% chance to 3HKO
252 Atk Garchomp Earthquake vs. 252 HP / 0 Def Mega Kangaskhan: 163-193 (39.3 - 46.6%) -- guaranteed 3HKO
Uninvested?
252 Atk Garchomp Earthquake vs. 0 HP / 0 Def Mega Kangaskhan: 163-193 (46.4 - 54.9%) -- 66% chance to 2HKO
252 Atk Tyranitar Crunch vs. 252 HP / 0 Def Mega Kangaskhan: 135-159 (32.6 - 38.4%) -- 98.2% chance to 3HKO
252 Atk Tyranitar Crunch vs. 252 HP / 252 Def Heatran: 102-121 (26.4 - 31.3%) -- guaranteed 4HKO
Uninvested?
252 Atk Tyranitar Crunch vs. 0 HP / 0 Def Mega Kangaskhan: 135-159 (38.4 - 45.2%) -- guaranteed 3HKO
Uninvested in defense, mega kangaskhan holds his own with both these epic tanks of the OU class. While yes, he lacks many of the resistances that these carry, he also lacks the weaknesses. Khan has more freedom to switch in and isn't meant to wall, so this bulk suits him exceptionally well to protect him from priority and the few pokemon that can outspeed him without fearing an OHKO by sucker punch. Remember, he is doing this effortlessly in a job I'm not even investing him for, he just carries bulk because bulky khan does it's job fairly well.
On the offensive side, we'll ignore the special stat. 125 attack with an essential choice ban bonus and 100 speed. Again, both stats are good, but nothing game-breaking by themselves. The 125 attack, however, might as well be recognized henceforth as 125x1.5 or (252 invested Jolly, since low balling makes better arguments) 523.5 (including parental bond boost). For an idea, this is more than Kyurem's adamant set without a band (since obviously base 125 with band is essentially parental boost).
But this attack in itself, while more than Mega-gengar's was unboosted, isn't even that bad since it gets worse. Mega kan's boosting move will give it +2 with relative ease, sending it only comparable to mawile after a swords dance (and actually more...)
1356 is Mega Mawile's +2 attack.
1396 is Mega kan's +2 attack.
That, dear players, is madness.
How? Parental bond acts like a choice band and therefore gives you an extra step. Don't believe me? Test it out. Band Mega Kan+2 will do the same as parental bond +2 but more than Mega kan (no parental bond) +3. The damage is actually equal to non-parental bond Kan +4.
Remember Mawile's flaw is speed, semi-limited move pool and 4mss. Kan runs base 100, a good speed tier to say the least given he also has priority to boot. Kan also can get near-perfect coverage and has a move pool to hit what he wants to (and basically everything with a dark/fight/normal set) for at least neutral damage. If heatran is an issue, Kan simply adds earthquake. Ferrothorn/Skarm? Fire punch. Cofagrigus and other ghosts trying to stop him? Crunch. He's so damn versatile, it is really a hard pokemon to even determine a decent switch to after preparing.
You've seen the damage calculations, there isn't much to argue there. This is just a simple explanation of why it is. Previously, the only other way to achieve this was to be tricked a choice band onto a +2 or to baton pass +2 to a band.
In a good sweeper for OU, sweepers generally have one or two of the following requirements:
Good->Great attack
Can find time to set up
Can outspeed multiple targets that could kill it
Can take hits from priority
Has priority
Great coverage
Other sweepers (just a few of the good):
Alakazam: Great attack, takes one hit, doesn't set up, but can outspeed most targets. Very good coverage
Garchomp: Can generally set up, very nice attack, can outspeed targets and might take a hit or two. generally good coverage (EdgeQuakeRage)
Lucario: Great attack, has trouble finding time to set up, has priority, does not take hits. Doesn't outspeed much, either. Very good coverage (Fight/Steel/Dark currently unresisted afaik) (mega lucario is different, but I suspect we'll be debating him soon...)
Gyarados: Good attack, doesn't outspeed before attack, can force a switch with intimidate (situational...), no priority, can take some hits. Coverage is meh... (EQ/Waterfall/Bounce or possibly just two...)
In megas?
Lucario-mega: Outspeeds a lot, still struggles to take hits, sets up easy and great coverage. Good priority. (But this is an ubers candidate as well, so). Has to come in safely to set up.
Garchomp-mega: Slow, same coverage, a bit bulkier, monstrous attack, no priority, still revenged easily enough. Before mega, must find safe switch.
Alakazam-mega: Fast, fantastic attack, no prioirty, basically dies to anything faster, still good coverage. Always must have safe switch.
Gyarados-mega: Bulky, decent coverage, slow, no priority, good attack (average for mega), doesn't necessarily need a safe switch.
All above has some flaws. Khan not only does all of what was listed, he also effortlessly plays wall breaker along with his sweeper set. His natural bulk, I feel I've adequately showed. His attack, I've also showed him stacked to mega mawile. And dark/fight/normal's resists? N/A.
So how have people been countering mega-kangaskhan? I sure hope you've been reading the main kan thread, but the general consensus was sableye for his prankster willowisp. The other options, cofagrigus, ferrothorn, skarmory, all take SE from some hit so Ferro and skarm have rocky helmets to prevent boosting on them. Cofagrigus can hard stop him with mummy and that insane physical stat, but how many people really actively like using cofagrigus?
Sure, rocky helmet garchomp/ferrothorn are decent stops, but how hard are either to take out without having kan do it for them? And should you realistically HAVE to run a rocky helmet garchomp/ferrothorn? Are these sets decently viable outside their job to basically sacrifice themselves so khan recoils himself to death? Not really. I don't remember signing up to have essentially a thorny porcupine slot on my team.
The amount of shifting and unconventional counters needed to possibly stop khan are also rather unfair. Skarmory, ferro aren't bad pokemon to use but when I have to run them with helmets simply to their job, that seems a bit defining. Wasn't I suppose to run shed shell skarmory to stop mega gengar from trapping me, and now I want rocky helmet to stop khan from killing me...
Checking isn't much better. You have to have a faster user who resists dark and outspeeds to kill it. Why? Because priority mach punch isn't killing khan.
252+ Atk Life Orb Technician Breloom Mach Punch vs. 0 HP / 0 Def Mega Kangaskhan: 283-335 (80.6 - 95.4%) -- guaranteed 2HKO
The faster pokemon than Kan possessing fight are: Mega lucario, infernape, the musketeers. Lucario can OHKO.
However, Keldeo cannot in the timid set needed to ouspeed mega kan. Virizion's stronger special side (using inconsistent focus blast) cannot guarantee it. Nor can Cobalion.
252 SpA Keldeo Secret Sword vs. 0 HP / 0 Def Mega Kangaskhan: 278-330 (79.2 - 94%) -- guaranteed 2HKO
252 SpA Virizion Focus Blast vs. 0 HP / 0 SpD Mega Kangaskhan: 306-362 (87.1 - 103.1%) -- 18.8% chance to OHKO
252 Atk Cobalion Close Combat vs. 0 HP / 0 Def Mega Kangaskhan: 306-362 (87.1 - 103.1%) -- 18.8% chance to OHKO
This leaves terrakion, Mega-lucario and infernape (who goes 96-100+ with cc) to OHKO Kan consistently while resisting sucker punch.
I think this evidence adequately shows that Kangaskhan is just to much for OU.