Boss levels

Every 50 levels there is a boss level (50, 100, 150 etc.).

In a boss level every enemy will attack your graveyard and try to destroy it. It includes police and the variants of the army, If it is destroyed you have lost this level.

In a boss level there is an additional enemy, which is not present in normal levels, a tank, see Tank

How much health and damage it has is currently unknown.

After you beat the level it said" VIP killed, new trophy acquired!" Although there isn't any VIP in the level.