I have been thinking, since most of the game is going to be up on the surface, I thought I would add a forest/grass terrain. It is basically a small green patch of plants, which act very simular to solid rock, except dwarves may dig through with their axes.
You can claim the tile, and build traps/doors on the tile, and only a secound lair or hatchery may be built on these tiles.
Nature lover-type creatures like fairies and pixies love to spend all their time in these land tiles, and nature haters like bile demons and black knights hate these patches, and will try to stay away from them, even if it means not having a lair, or eating.
If 9 or more tiles of grass is all around in a square, the tiles start growing trees. Trees can get it your way really easily. They can't be digged out by your imps because your imps axes are too small and weak, and therefore, no creature can pass them. However, Dwarves can digg through them with their strong axes, and let them pass through. each tile gets one tree, like a baracade mixed with a solid rock, and trees become harder to dig through the more water is around them
Keepers that control them have nothing growing, unless it is next to a water, or in a wet or rainning realm. the tile give 2 mana per secound, and nature lovers like fairies, pixies, and others will build lairs, and spend most time around the tiles.
it basically looks like any pile of small grass when controled by the good. When any keeper has claimed it, they use the magic of their dungeon to change the color to the keeper who owns them, weather it be green, yellow, red, or blue. If no one owns it, it looks like a pile of dead grass, like a patch that hasn't been watered ever.