Board Thread:General Discussion/@comment-8505655-20130507211744/@comment-10870881-20130708060129

1. Ben said that he was afraid of his Ultimate forms, which was justified eventually.

http://ben10.wikia.com/wiki/The_Ultimate_Sacrifice

My theory is that either afterwards Ben was afraid to use any more Ultimates because they might become sentient too, or Azmuth disabled all further Ultimates he hadn't already used. And Ultimate Way Big was unlocked off screen earlier or given to Ben before fighting Diagon.

2. They never said that they had a predator for every alien, they are just shown scanning a bunch. and Ben always seems to turn into the same few aliens instead of using ones that haven't had predators shown. Which either suggests that Ben is an idiot or that the Omnitrix reacts to the Nemetrix badly.