Best alien is XLR8 AND heatblast. When you do damage he go up some tower. There are many of them. There is a button under each one. If you do sufficient damage he will start to climb. Use XLR8 in this and press the button under the tower he is on after that their is a minigame. Do this three times and finish all three minigames and you have defeated him.
Hope this helps. P.s he keeps jumping of one tower to the other so prees the button fast. I recommend XLR8.
First to beat ghostfreak you have to change to fourarms and us the tombstone pu-nch that will take ghostfreak out of his form.then change to wildvine and pull the glowing handle if you do this when ghostfreak is in a form it will do nothi-ng and you will be an open target.