One of the reasons Mega Kanga is (In my opinion) broken for 1v1. Is fake out is a huge threat in 1v1, and always has been. Mega Kanga is the only pokemon that can virtually fake out for free damage against ANY pokemon that isn't rocking protect/spiky shield & king's shield/inner focus. If the pokemon is not ghost, you hit it with stab parental bond fake out which hits HARD. If it is a ghost type, you can stay as Scrappy Kanga and hit it normally. Mega kanga remains the only fake out user with scrappy. Which also assures it a free safe transition into Mega form practically every time. And that is assuming it is even running scrappy to begin.
It can run early bird to counter sleep spammers which are all so common in 1v1. Or inner focus to protect itself from faster fake out users. Typically in 1v1 the second you see the pokemon come out you know what ability it is running. For Mega Kanga it can be a guessing game, and this is even furthered farther by its HUGE movepool.
Not to say there aren't counters, Cofagrigus, Avalugg work well against it. I typically run a stalling Gourgeist, sableye, or Mega gardevoir to counter it. Its just seems in the process of switching to counters I lose out on a lot of the power I wold normally use in my classes just trying to counter one pokemon.
Edit: After trying the Avalugg set it was rather good, but kept dying to Mega Kanga w/ Seismic toss. Fakeout then two seismic tosses take out Avalugg no matter how high your defense is.
Edit:Edit: Also Guts Conkeldurr with Protect is a phenomenonl counter. Protect first turn protects you from fake out which also activates the flame orb. Then Drain punch/mach punch ftw.