For the
Special Level, you will have to complete it until you hit
Wave 30 and clear it. Achievement will not unlock during play, but when it is game over, it should unlock.
It is very similar to their achievement in the
Quantic Pinball game, although technically there is no timer this time ticking down for you to clear the level. In this level skulls are coming down and you need to clear them before they reach the red line at the bottom of your screen. Once one is halfway through the line, it is game over .. see screenshot:
Best way is to get multi-ball activated as soon as you can as it makes a big difference. I found using two balls easier to control and clear the level than when you have all three active.
For those whole played Quantic, this achievement is easier to obtain than their similar Tsunami one.