Rocky terrain, which is difficult enough to walk on that you must go around it or levitate or fly over it, but permits magic and items to pass over it.
Add “collapsed corridor” and “cracked wall” terrain types. These act mostly like solid rock and solid wall, except that if you attempt to move onto it you can, if you would be capable of squeezing past a boulder. Would be more useful if a light, stealth-based character build that ordinarily carries little enough stuff to squeeze past boulders were viable.
Not specified which characters these would use in text-based windowports.
Add Sokoban levels with a pinball-inspired mechanic: some of the walls are a new “bumper” terrain type. An object or creature that moves into a bumper will be hurled away from the bumper in a non-random direction (which could be straight back in the direction it came, always at a 90 degree angle, or vary based on the particular bumper). The puzzles involve moving boulders into the bumpers to propel them in ways regular pushing can’t accomplish.
New “flooded stairs” terrain type. They act normally as stairs, but are also treated as three-dimensional water (that you cannot fly over and must be submerged in, like on the Plane of Water). This would not be very useful on its own but would be a building block for quests or other special levels that are entirely underwater.
Grass terrain, rendered as a green period or comma. It could have the following properties:
Slope terrain, which is a terrain that appears like walls but does not block line-of-sight. It blocks movement unless levitating or flying, and cannot be dug down on or into. If you somehow get onto slope terrain (such as by stopping levitation while on it), you can move off it in any unblocked direction. This would allow interesting level designs like pyramids and switchbacks. Is still a bit problematic without implementing actual height values for the terrain, since for things like a large pyramid, you would be able to see straight over the top of the pyramid and down the back side.
A new type of “fence” terrain that is like wooden iron bars: it cannot normally be moved onto but it can be burnt or kicked down, and it does not block line of sight.
New type of terrain, “fire terrain”, a square that is on fire. It displays as an orange period. (If this will be too nasty to people who play with color off, the glyph should perhaps be changed.)
Greasy floor, a new type of terrain (or perhaps a trap?) that applies grease to any boots you are wearing and almost always makes you slip. Slipping on greasy floor (which can also happen by walking barefoot or with already-greased boots on) causes you to drop random items, some of which may get greased.
The player can create greasy floor by smashing a potion of oil or applying (multiple?) charges from a can of grease to the floor.
Creatures that move onto a greasy floor patch may “slip and slide and struggle to stay upright”, losing their next turn 70% of the time. This also happens to a creature standing on a greasy floor patch that tries to do something involving footwork (combat, moving off the square, etc) 30% of the time. Or for a more simplified implementation, the trap doesn’t have to cause loss of turn when moved onto (though it might still produce a message), but has a 70% chance of making the creature lose its next turn regardless of the action (still need to keep your balance to take out a scroll to read or zap a wand, for instance).
If implemented as a trap, it cannot be untrapped (except probably by the standard method of digging a pit on it), but will eventually wear out after a slightly randomized number of times it affects something. (This prevents you from setting a single one in Ludios and then standing back to watch the whole army get greased and fall over themselves.)
Quicksand, either as a trap or terrain type (they both have advantages and disadvantages); stepping in makes you start sinking in like with lava, and if you don’t find some way to get out in time, you suffocate to death.
When you hit a tree with fire from any source, it can turn into a burning tree (red #). This burns for a few hundred turns before burning out and turning into normal floor. While on fire it acts as a light source of radius 9, and deals fire damage to anything adjacent each turn and occasionally to anything within a radius of 3. Come to think of it, there could also be a “bonfire” terrain using the same glyph.
New “hedge” terrain, green #. It blocks movement but not line of sight (like iron bars), can be chopped down with an axe, and has a chance of blocking ranged weapon attacks passing through it. Possibly it can be jumped over.
Mud terrain, brown }. It can be walked on, but if you stand in one spot for long enough you will start sinking into the mud. You will be able to pull free if you are only a little stuck, but once you get more stuck you cannot, and if you cannot extricate yourself somehow you will eventually sink below the surface and suffocate.
This might best be implemented with a new “mud pit” trap, which gets created by standing on mud for too long and works similarly to a regular pit in that you are held in the same place by it for a while as you try to move out. Except a mud pit allows you to sink down and suffocate.
Pool of acid terrain that deals severe damage and corrosion if you fall in.
Sand terrain, which slows you down a bit when you walk on it. Shows up in certain special levels. Might be a yellow . glyph.
Glass doors that you can see through and kick to break with ease.
Slime terrain or puddles of slime, left behind when P-class monsters move around. It either deals damage or erodes footwear to stand in it.
Water lily terrain: can be walked on, but if burned, rotted, or dug on, it turns to water.
Dirt terrain, behaves the same way as stone but digs faster.
