Back with a Vengeance is the greatest way to cap off a season. As usual, Ben is messing around with the Omnitrix (didn't he learn his lesson from the last episode) This time, he is more successful as he accidentally finds the master control for the Omnitrix. Now, he is able transform into any of his alien forms at any time for as long as he wants. And its a good thing to...
...Because Kevin 11 and Vilgax have officially "teamed up". They find Ben and attack him. Grandpa uses a null void projecter to send them both to the Negative Zone. Unfortunantly, Ben was caught in the crosshairs and sent to the Negative Zone too. Now Ben must fight against two of his enemies along with the many dangers in the Negative Zone.
Eventually, Ben, with help from Gwen, escape, but not before the Omnitrix was maxed out and now Ben is back to square one.
A great way to end the second series.