Survivor class is quite overpowered, survivors almost always beat out other classes in kills and has a very overpowered combo special. I found a way to grind the combo special with blade traps and shotguns which allowed for me and my friends to easily beat all levels. I had a few suggestions for survivor. Instead of having a timer kill ball, the ball could just detonate once killing nearby enemies. This would have about the range of an advanced blade trap. Another idea is if the kill ball is kept, a simple way to make it harder is to increase the amount you need to combo. This could be an issue though which might require more time to the combo length. Those ideas were to help keep the Survivor as a horde slayer however, maybe the combo special could be a shield for players which lasts either 7 or 10 seconds.