Ben 10 Omniverse

Before you fighting Malware by first time, there is a puzzle to be solved with Feedback, if you not solve the puzzle, enemies spawn infinitely, are really easy to kill them. It's possible to upgrade all the characters in that way too.

Feedbackis a character you have unlock during the 2nd level. All you need to do is defeat 50 enemies with any attack you choose and the achievement will unlock on the 50th defeated enemy. This transformation can drain the electricity from one of the enemy types leading in an instand kill, which can be fouind on level 4 or 6 quite often so use these levels to gain easy kills for Feedback.