There is no combat in the game. If you touch an enemy, you get hurt. However, there will be a wider variety of traps, enemies and behaviors to watch out for. For instance, a skeleton might just wander around aimlessly, while a spike trap will pop up at specific intervals. There could even be enemies which stand in one spot, looking around, and if they see you, they'll charge at you at top speed. The entire game is about timing and exploiting how the enemy works.
The purpose of the game is to get pellets, and pellets are both you experience points and you money. You can spend pellets to buy keys, items, and abilities from shops (since there is a static number of pellet, care must be taken to ensure that you can't buy the wrong stuff and not have enough pellet-money to progress... perhaps a use for Mechanic #004 - Environment Tree?).
The game also keeps track of how many pellets you've collected total, and certain areas of the game will be closed until you reach a certain count. For instance, the castle may require 10,150 pellets to enter. Once that number it hit, the draw bridge will go down and you can enter.
Dungeons are a special type of zone which are separate from the world map. Upon entering a dungeon, you are forced to get every pellet on each floor before the entrance to the next appears. As such, it is sort of like an arcade game with individual levels. At the end of a dungeon is a boss type event, and defeating that earns you a new ability. Like a Zelda game, there might be a dozen or so dungeons around the map of varying sizes and difficulties in addition to the already sizable world map.