Extraordinary ability, to be used on a helpless, intelligent target.
One attempt takes two hours. First, roll 1d20+Cha against a DC equal to the target's HD thrice. If you succeed all three times, you have broken the opponent's mental defenses, and have complete access to his mind. If you fail at least once, the attempt fails - you can retry again. If you fail three times, you have provoked a defensive reaction: You and the subject roll an opposed check of 1d20+highest of Int,Wis or Cha, with the subject getting a +5 circumstantial bonus due to it being his own mind. Whoever loses takes 1d4 Int, Wis and Cha drain due to permanent brain damage.
This ability can be in theory used an arbitrary amount of times per day, though time considerations limit it to twelve, and most cubi who have ever done it will tell you that once a lifetime is too often.