And here comes the arrogance!
There are risks associated with using PuP on the turn Kangaskhan MEs. For one, not every Pokemon that Kangaskhan switches into will be at low HP and / or weak to PuP. Second--and you even mentioned this lol--Kangaskhan may just have to remain in its current state to weaken a ghost with Return / Double-Edge; if Kang Mega Evolves and uses Power-Up Punch while a ghost / Chomp / Fighting resist is still alive and healthy, then it's not going to be dealing much damage, let alone sweeping a single thing. Third, there ARE times at which Mega Kangaskhan is better off using its coverage move or STAB than it is attempting to boost. Lastly... you generally don't play your win condition so aggressively lol.
Alright, so lets do this.
Garchomp:
252 Atk Parental Bond Mega Kangaskhan Power-Up Punch vs. 4 HP / 0 Def Garchomp: 67-79 (18.7 - 22%) -- possible 5HKO
+2 252 Atk Parental Bond Mega Kangaskhan Sucker Punch vs. 4 HP / 0 Def Garchomp: 265-313 (74 - 87.4%) -- guaranteed 2HKO
Total: 92.7% to 113%. KO'ed by Power-up Punch + Sucker Punch. Garchomp isn't gonna get one turn to do anything, especially if any hazards are on the field. What about a revenge-kill? What can Garchomp do with the 1 turn it outspeeds Mega-Khan (forcing Mega-Khan to use +2 Return for the OHKO):
252 Atk Choice Band Garchomp Outrage vs. 0 HP / 0 Def Mega Kangaskhan: 294-346 (83.7 - 98.5%) -- guaranteed 2HKO.
+2 252 Atk Parental Bond Mega Kangaskhan Return vs. 4 HP / 0 Def Garchomp: 508-598 (141.8 - 167%) -- guaranteed OHKO
Woops, Choice Band Garchomp isn't even a clean revenge killer. Mega-Khan kills itself due to Return self-inflicted damage from Rough Skin, but easily kills Garchomp with +2 Return. Chances are however, Garchomp isn't going to use Choice Band Outrage anymore, lest he be Togekiss setup bait.
Fighting Resist? You mean Lugia? I've already posted the calculations for
LUGIA UBER-WALL earlier, and that 4x fighting-resist wasn't good enough to take on Power-up Punch + Return from Mega-Khan. Any fighting-resist with less defenses than Lugia is going to lose to Khan. For example:
+2 252 Atk Parental Bond Mega Kangaskhan Return vs. 252 HP / 252+ Def Reuniclus: 420-496 (99 - 116.9%) -- 93.8% chance to OHKO
Ghost? I already told you, Khan requires prediction to win. Which is why I'm
focusing on Ghosts in my discussion. Nonetheless, `Khan does quite fine against Ghost switch-ins. All he has to do is Mega-Crunch on the switch-in and then do it again for the kill.
252 Atk Parental Bond Mega Kangaskhan Crunch vs. 252 HP / 252+ Def Trevenant: 219-258 (58.5 - 68.9%) -- guaranteed 2HKO after Leftovers recovery
252 Atk Parental Bond Mega Kangaskhan Crunch vs. 252 HP / 252+ Def Jellicent: 231-273 (57.1 - 67.5%) -- guaranteed 2HKO after Leftovers recovery
252 Atk Parental Bond Mega Kangaskhan Crunch vs. 252 HP / 0+ Def Gengar: 354-417 (109.2 - 128.7%) -- guaranteed OHKO (Sub-Disable set, max HP / Max speed)
252 Atk Parental Bond Mega Kangaskhan Crunch vs. 252 HP / 0 Def Aegislash-Shield: 180-213 (55.5 - 65.7%) -- guaranteed 2HKO after Leftovers recovery
Aegislash has the most issues because of King's Shield. On the 2nd turn, Khan can simply use Sucker-punch to deal with Aegislash, and then follow up with Crunch since King's Shield will probably fail on the 3rd turn. Khan fears no Swords Dance or Weakness Policy because he's faster than Aegislash and immune to Shadow Sneak. The standard Khan strategy only fears Automatize + Weakness Policy, but can spam Sucker Punch against them or outpredict with Crunch on the Automatize.
If you don't like that "mind game", then run Earthquake for the easy KO, even against Automatize + Weakness Policy (Crunch on the switch-in, Earthquake on 2nd turn to predict the King's Shield... KO's the Aegislash if they use Automatize, and King's Shield doesn't lower EQ attack).
Now, you've forced Khan to be at +0 by saccing a Ghost, and can retaliate with a _real_ revenge killer, like Meinshao or Terrakion. Mega-Lucario survives a +0 Power-up Punch and OHKOs with Close Combat or +2 Vacuum Wave as well, potentially setting up for a mega-Sweep... (which is why I suggest Earthquake on Khan). But its important to remember that to
get to this point, you had to sac a ghost pokemon.
Another potential "out", (which is why I suggest to run Earthquake on Khan), is Mega-Lucario. Mega-Lucario's battle-plan is "sac a Ghost" to ensure Khan is at +0, use Nasty Plot on the mega-Evolution turn, and KO with Vacuum Wave.
252 Atk Mega Kangaskhan (70 BP Fighting Attack) vs. 4 HP / 0 Def Mega Lucario: 166-196 (58.8 - 69.5%) -- guaranteed 2HKO
+2 252 SpA Adaptability Mega Lucario Vacuum Wave vs. 4 HP / 0 SpD Mega Kangaskhan: 368-436 (104.5 - 123.8%) -- guaranteed OHKO
70BP Fighting Attack simulates the effect of +0 Power-up Punch. So... Lucario survives a +0 Power-up Punch, and gets a successful Nasty Plot. Then, it OHKOs Mega-Khan with Vacuum Wave, and can potentially sweep the opponent. But Khan can stop this potential reversal by just running Earthquake. Or... switching out to another team member.
So Mega-Khan's strategy is so braindead simple. Use Power-up Punch on turn 1, or if you predict a Ghost, use Crunch instead. Outside of Sableye, Eviolite Dusclops, and Gorgeist, you are going to 2HKO all of them with Crunch. Eviolite Dusclops and Gorgeist is 3HKO by the Burned Mega-Khan however, and therefore are not considered counters. The only true counter is Sableye who has access to Prankster Will-o-Wisp and Prankster Recover. (Recover off the damage, and watch `Khan die).
The ONLY time Khan needs to play careful is if the opponent has Sableye. Otherwise, if he gets to +2, he basically singlehandedly wins the game for you.
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Now, please, enlighten me. What magic strategy do you have against Mega-Khan? You keep telling me losing strategies that have been analyzed through dozens of pages of discussion already. You don't even seem to understand why `Khan's first turn is almost always Mega-Evolve + Power up Punch...