Bridge Constructor: The Walking Dead

Pretty straight forward - you need to get a total of 100 kill across completed levels in the game. You can track your progress by going into chapter select and looking at the tally on the bottom right. There are a total of 499 possible kills so you should have no trouble hitting 100 if you are just playing through the game normally

An important note is that kills cannot be farmed meaning you can't just replay the same level over and over to rack up kills and they don't count unless you complete the level. Replaying levels is fine however your kill count will only increase by the difference in walkers killed. Meaning if you killed 10 on your first time completing the level and the second time around you kill 20, your total increases by +10