Ben 10
39 Achievements
1,000
6-8h
Omnitricks
You've shown mastery over the Omnitrix by using all forms in one fight.
30
21.22%
How to unlock the Omnitricks achievement in Ben 10 - Definitive Guide
As the description says, you must kill an enemy with each alien in one fight. Find a fight where there is more than 10 enemies (the second fight in The City is a good one as there is way more than 10 enemies) and take turns killing an enemy with each of the aliens so that all 10 have a kill to their name by the end of it. Once you have registered a kill with each alien in one fight, the trophy will pop.
Note: This one actually popped for me in a good way after I had made a kill with Stinkfly as he was the last alien I killed something with, so while it wasn't all 10 killing enemies in one fight, it was just in overall in general.