Allow me to preface my augment with something: I have played a LOT of Hackmons. "What in the he'll does Hackmons have to do with a debate to ban a Pokemon, no less a Gen. VI one?" you might be asking yourself. The answer in short? Everything. Hackmons may seem like a shitty tier with a lot of gimmickmons, and you'd be right. However, once you get to the top of Hackmons, gimmicks won't cut it. There are very well designed teams that take advantage of everything under the sun, making each battle uniquely challenging. One of the strongest strategies I've seen in Hackmons is Shadow Tag Perish Song Giratina. Allow me to remind you, this is a tier where Wonder Guard Spiritomb, Jolteon, and Scizor are available. This leads to a great number of stall tactics, and the greatest user of those is none other than Giratina. While M-Gengar may not have nearly the amount of bulk that Giratina has, it has some other advantages: 1. It's not Hackmons, so it can run attacking moves if the need arises. 2. Its glorious speed. As many others in the thread have pointed out, it takes a lot to outspeed this thing,and this allows it to pull of this strategy even better. 3. The inability of counters to come in on it. If you have a counter for M-Gengar, good luck bringing it in. Unless your team is mono-ghost (and even then there are a bunch of issues with that), you cannot switch out. As soon as Gengar can come in on you, you have recieved a death sentence. And if your opponent is using perish-trapper Gengar, they'll know how to use it. I belive the reason something should be banned it that it is uncounterable. If there is a Pokemon that has no effective counters, then more than one Pokemon on a team will have to be dedicated to stopping that threat. At that point, it has become "overcentralizing" and creates a shitty meta. Instead of having 4drag2mag, you'd have 2drag2mag2M-Gengar checks. It would stifile team variety, usability, and does not contribute something that cannot be replaced (Wobby/Gothitelle). That is why M-Gengar should be SHADOW-banned from OU.