Ben 10 Omniverse

XLR8 is a character you have unlocked at the start of the game. 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 is rather quick attacks as the achievement suggests which comes in hand if you want to use XLR8 to go for the combo achievements also.

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.