NPC AI Mechanics - Movement

Hello,

I wanted to discuss different types of NPC AI mechanics. Particularly when it comes to movement on a fixed board. Their AI when it comes to combat is fairly simple. If their movement brings them into contact with a player's characters, they will always stop and attack.

Imagine movement in the game as being controlled by normal APs. Give these NPC 3 AP each, with a maximum of 3 NPCs on the board at any given point in time. The board is a 15x15 grid. 1 AP to move forward, 1 AP to turn 90 degrees. These NPCs have 3 spawn points on the board equidistant from eachother (players start on opposite ends of the board). The board is not an open space and will have various obstacles that prevent movement through and rough terrain that slow movement.

I am aiming for a very simple and quick way of determining movement for these NPCs. Also need a way that prevents them from a) clumping and b) always heading to the edges of the board.

Here are the different options Ive been playing around with:

1) Roll d6 (Simple, quick, non-interactive). The dice determines the direction and type of movement:
1- move forward.
2- turn right, move forward
3- turn left, move forward
4- turn around, move forward
5-6- spawn more enemies
If NPC encounters and obstacle, stop movement. Im afraid that this type of movement may cause the NPCs to aggregate to the edges of the board. It makes them rather unpredictable as well. Given the type of NPCs they are, that is not a problem. They dont need to be particularly smart or aggressive.

Also, with rolling a D6. I believe that rolling it once for each NPC (even if there are only 3) may bog down the game. If each NPC spawns with a different facing, it wont seem that they all move like synchronized swimmers even if they all follow the same die roll.

2) Pre-designated movement path (Simple, quick, non-interactive). NPCs move on the board along pre-determined paths. Im not sure I like this one at all. Ive seen it used in Arkham Horror and Munchkin Quest and something about it bugs me. First being that it clutters the board with too many colors and symbols. Second being that it is much more predictable. I cant wrap my head around making this work.

The only system of this type that I do like is Battlestar Galactica. I dont see something that deterministic working for a grid map.

3) Card based movement (Moderate complex, relatively quick, somewhat interactive).
a) Card deck with movement icons on it. There is no central deck to the game (like Arkham Horror or BSG) and creating one simply for moving NPCs seems a bit like a waste. However, it could be done and it would allow a number of possibilities for movement beyond the 6 options available on a dice roll. I could have each card with 3 different move determinations on it (one for each NPC), which would prevent the synchronized swimmer syndrome. Still very random. I could also have the cards with simple AI for handling interaction with obstacles listed on the card. Simple iconography showing how an NPC will react if it hits a wall for this card draw.

The more I type this out, the more I like this option.

b) Based on player card plays (increases interactiveness and complexity). During a game turn, players will be playing cards to alter results of actions. I could imprint on each of these cards a movement icon for the NPCs. Whenever a card is played, it "programs" the NPCs to perform that movement. At the end of the players turns, run through the cards that were played and move the NPCs based on the icons.

I like how this allows the players to somewhat determine how the NPCs move. Adds some good interactiveness, even if it does up the complexity and can bog down the game a bit. It adds another layer of decision making to playing cards. It can be made to fit thematically to the game easily.

Those are the options Ive come up with so far. Any other ideas? Comments?