This thing needs to go to ubers. "Pray my opponent is stupid/not running X move" should not be a strategy to beat it. On its own, it does stupid amounts of damage even to things that resist Return but aren't necessarily physical walls (such as max HP Scizor). But I've seen several strategies involving team support with this thing (such as Scoliopede, Ninjask, or Smeargle baton passing to it; Tailwind/Sticky Web support; Wish/Heal bell/Healing Wish support; Trappers such as Wobbuffet or Gothitelle to remove its checks, etc) which turn it far more broken than anything suited for OU using these strategies. Fire Punch, Ice Punch, Crunch, and EQ have been becoming increasingly common on it to remove typical physical walls.
From the other end of the spectrum, I've been seeing a fair amount of otherwise asinine sets on things in hope of beating this thing. For example, physically defensive Rocky Helmet Garchomp (why would you run this over Lum Berry/Band/Sash/Scarf/something else and an offensive set, except in hopes of checking Khan?), Will o Wisp on completely random things that happen to get it, Rocky Helmet and/or Counter on random things in general, etc. While these things aren't necessarily useless vs. teams that do not have Mega-Khan, they are usually sub-optimal to the goal of the teams that they are on, and as a result turn into near-dead weight vs. many other teams.
On a side note, Scarf Ditto has been an amusing check to this thing. I've killed off many Khans, using their own boosts against them. It doesn't really suit most teams, and depends on the opponent not being a major idiot (and therefore running a reasonable set) to work in general (whether or not Khan is around).
Tl;dr - Mega-Khan has turned OU into a shit show, ban please.
Some more relevant calcs:
+2 252+ Atk Parental Bond Mega Kangaskhan Return vs. 248 HP / 0 Def Scizor: 267-315 (77.8 - 91.8%) -- guaranteed 2HKO <-- typical ev spread, not meant to be a physical wall, but closest thing to "defensive" on many HO teams
+2 252+ Atk Parental Bond Mega Kangaskhan Fire Punch vs. 252 HP / 252+ Def Skarmory: 300-354 (89.8 - 105.9%) -- 37.5% chance to OHKO <-- so much for a check
+2 252+ Atk Parental Bond Mega Kangaskhan Fire Punch vs. 252 HP / 252+ Def Ferrothorn: 624-738 (177.2 - 209.6%) -- guaranteed OHKO <-- lol
+2 252+ Atk Parental Bond Mega Kangaskhan Ice Punch vs. 252 HP / 252+ Def Garchomp: 780-924 (185.7 - 220%) -- guaranteed OHKO <-- Goodbye
+2 252+ Atk Parental Bond Mega Kangaskhan Ice Punch vs. 252 HP / 252+ Def Gliscor: 648-768 (183 - 216.9%) -- guaranteed OHKO <-- yep..
+2 252+ Atk Parental Bond Mega Kangaskhan Crunch vs. 252 HP / 252+ Def Cofagrigus: 309-366 (96.5 - 114.3%) -- 81.3% chance to OHKO <-- :(