The Color Defense game is in a tolerable state right now: not quite a game, but very close. The growing board works -- only in one direction, but I'm still agnostic about how it's going to grow -- and the opponents can move around the board based on the expected speed on that square. With the addition of a basic tower type and the conducting walls, it will achieve game status.
(1) The growing board. The board grows as the game is played. Right now it grows after every site empties, and in only one direction. Both of the rate of expansion and the directions of growth are up in the air:
(a) Rate of Expansion. Growth should be associated with the size of the player's tower complex, possibly six squares beyond the player's farthest tower on each side. Currently it grows each time a site empties, which grows the board much too fast -- especially with recursive path finding.
(b) Direction of Expansion. If size is based on extend of player's building, then the board has to grow in different directions. Probably, it will grow one row or column per site spawning until it reaches the safe range.
(2) The player's towers. Towers must be powered by colored source sites, but mixed towers will be possible. Towers will not conduct power, but walls will.
(a) The Sources. There will be three colors of source -- blue, red, and (probably) yellow. Each source will have a power rating, and will power towers of that color up to that power rating. Sources not at their maximum rating increase one point per wave until they get there.
(b) The Towers. There will be different groups of towers for each of the different colors. These towers will have different powers. Blue might be an ice slick, red might be a gun tower. There will be mixed towers, as well, that you can buy later on, that mix these abilities -- freeze rays, for example.
(c) The Walls. Walls will both protect the player's complex and conduct power. Each type of power conducted with strengthen the wall against attacks both in general and against creeps of the same color.
(3) The creeps. The creeps are attracted, mainly, to sources of their own color. The game proceeds until the creeps destroy all connections to active sources and the player cannot afford to reconnect active sources to his complex.
(a) Pathfinding. Pathfinding gets fairly slow when the distance between spawning site and targeted source gets large.
(b) Targeting. Sites should target the nearest connected source of the same color. Next best: nearest connected source of a different color.
(c) Damage. Creeps do damage when colliding with structures, eventually destroying them. When colliding with connected sources, it reduces power output; enough reduction destroys the source.
(d) Power Ups. When colliding with unconnected sources, creeps increase in power, possibly gaining powers as they power up.
(4) Upgrades between games. The player will gain currency during games that can be used between games for different purposes.
(a)The player's complex. The player will have a persistent complex that they can upgrade between games.
(b) The tech tree. The player will be able to buy different towers and upgrade their towers between games.