First I want to say that I've finished the previous Ben 10 game where the final boss is my favor Vilgax and my favorite alien heroes to deal with this monstrous guy is Heatblast or Fourarms. So I want to know who is the final boss of this game and which alien hero to use against him ?
It's the HighBreed. Spidermonkey or Jetray work the best on him since you need speed. Humongousaur is useless, Swampfire and Big Chill should be okay, but Spidermonkey and Jetray are the fastest and can work the best on him. You need to press circle on the computer, and you will be on the ceiling get in front of a switch, and then press circle in front of that. If you ever change back to Ben, make sure you are not near the HighBreed, because he'll kill you in one hit. After you do all that, hit the computer one last time to end the fight (with circle). And the HighBreed is invincible, so don't attack him, although you can attack the red pipes when he's near one to stun him, and there are Xenocites, but they aren't that annoying, so just concentrate on the switches and stunning the HighBreed if you must.