Starting in the cemetery, enemies will be walking about. To get the jump on them, walk up behind them and press X to hit them with your candy bag. If successful, our heros will quip and the battle will start with all enemies taking some damage.
If you do this correctly with every enemy encounter, then the 10th time will be in the mall, in the area under construction. If not, there are plenty more opportunities.
Enemies cannot be surprised at the door, only when you can walk up behind one. Some enemies can't be snuck up on, such as ones always facing you or hiding in the shadows (there is only 1 encounter like that in the mall).