You must complete the story first to unlock this mode.
-This is a time based mode and each wave is a minute long. You must survive the minute to advance.
-If you die at any point, you will restart from the beginning.
-After killing 30 enemies in a row (W/O taking damage) a random box will appear. Either health, weapon or power up will randomly appear.
-Using your RT power up not only clears out enemies but the countdown timer still continues. Use it only when you really need it.
-Utilize the enemies with their lane clearing abilities ( Dogs, Fat zombies, enemies with guns). This will help you a lot and will potentially clear the way for something bad up ahead. If you have cleared story mode already then you should be aware of the combos by now.
- Save your power ups for only when you TRULY need them, like when you know you cant avoid a hit.
-During the later levels it will speed up so you must react a little faster.
-The levels are not the same every time. Enemy placement and type will be different each time.
Lastly, PRACTICE! You may not get it on your first shot but it is not as hard as you might think. I personally got it on my 5th attempt. Once you reach level 10 the achievement is yours. You do not have to complete level 10.