Well if you have ECX RC2 you need to get enough PL.
then you land on the ground. This is important. Once you are STANDING on the ground press the button 9 and you will see an icon that looks like a fusion dance picture.
Press and hold the mouse 2 button. When teh bar charges you will be given 6 advanced melee arrows. You have 2 seconds to get them all right. If you get all of them correctly you will fuse into Gogeta for 5 minutes. If you get even 1 wrong you will get a fusion fail character with the PL of 1 and no attacks. This allso lasts for 5 minutes.
If you die fusion allso wears off.