- Mega Gengar has 130 base Speed, which is godly for OU
- Mega Gengar's Sp. Atk has the same power as Life Orb Gengar, minus the recoil
- Mega Gengar's ability, Shadow Tag, is by far the best and most broken ability in the game. Taking away the ability to switch is 100% unskillful, unfair, and uncompetitive. This guarantees Mega Gengar at least 1 kill with any set
- Mega Gengar also has access to Destiny Bond. When played right, Mega Gengar carrying Destiny Bond is guaranteed 2 kills when using Destiny Bond
Sounds pretty broken to me.