New magic beam trap, which fires a magic beam (probably implemented as a magic missile ray, or possibly a random ray type) from a fixed point several squares away in one of the eight directions towards the trap square.
Internally, the fixed point is stored in the trap’s launch coordinates, and the ray type should probably be stored as the appropriate wand type in launch_otyp.
Mummies have a constitution-draining touch attack, which possibly also inflicts a ‘withering’ intrinsic that deals damage over time and abuses Constitution every turn.
Mummies could also “cast” a curse on you, not to curse your items, but to make you sink through the floor, sending you down 1-3 levels.
Outside the Plane of Air (where there is no gravity), stepping onto air terrain automatically makes you fall to your death unless you are levitating or flying. (Or possibly you merely fall to a lower level, taking a fair amount of damage, or you have so far to fall that it takes a couple turns to hit the bottom, in which you have a couple turns to take some action to save yourself, by levitating or flying or whatever). However, you are prompted to confirm stepping out into the open air if it isn’t safe to do so.
Items dropped into open air either end up randomly placed on a lower level if there’s a sensible lower level to place them on, or vanish forever (though in that case an exception needs to be made for the unique items).
If falling into air is an instadeath, life saving acts the same as if you die in lava; it puts you on a safe location (“You find yourself back on solid land again”).
Air can use the W_NONDIGGABLE flag, or possibly one of the other struct rm flag bits, to represent a wind barrier, which the level designer can use to make a region of air impassible. Attempting to move onto such a space produces a message like “A strong gust blows you back!” and makes you lose the turn.
One of the greatest problems with air terrain is what ASCII character to display it as; existing implementations use just regular space (which is what it displays as on the Plane of Air), but this is easily mistaken for stone, which can lead to players unexpectedly falling to their death if there is no safeguard against wandering off a cliff, and would present a problem if there were ever a air/stone boundary, which would be invisible. Other suggestions include: space, but highlighted with the terminal’s black color ( ), black pound sign (#), black tilde (~), black right brace (}), or even just gray counterparts of these. All of these have various downsides; for instance, it must be expected that they will render as dark blue for some players who have use_darkgray turned off.
At some skill level (Skilled or Expert or maybe even Master) martial arts gives you two attacks.
Occasionally, when a bones file would create a ghost (e.g. most times), and the level difficulty is high enough, create a wraith of the player instead. If in Gehennom, occasionally create a shade of the player.
When a bag of holding explodes, each item inside has a 1/13 chance of being destroyed and a 12/13 chance of being scattered (using the same code that scatters drawbridge chains). Note that scattered fragile items such as potions are liable to break by crashing into things.
Amulet of drain resistance, which also gives immunity to death magic. Useful if monsters casting drain life are implemented.
Mindless undead are immune to every form of fear effect, including scare monster.
Note: EvilHack takes this a step further and makes every mindless monster immune to fear, not just undead. This may be more apt, depending on your point of view.
Add a knockback attack and a monster that can use it. Getting knocked back into a wall deals some extra damage, and getting knocked back into water or lava has predictable effects.
You can use stethoscopes (or possibly probing) on eggs to identify them.
Cancelled trolls won’t rise from the dead.
You can dual wield Sting and Orcrist; this gives an even bigger damage bonus against orcish monsters.
Monks can forcefight or kick boulders and break them with high enough Strength.
Grand Master martial arts skill allows you to (attempt to) force-fight boulders and statues to shatter them with your bare hands.
Additional temporary effects accompany drinking a potion of booze. The effects wear off when the confusion does (so if you extend it by, say, drinking a potion of confusion, the effects are prolonged). There is consensus that there should be both positive and negative effects; all of the following have been proposed:
Leprechauns (or anything with AD_SGLD) should steal items made of gold out of the hero’s inventory.
Scale monsters’ hit dice bonuses based on their size. In order to reduce the high amount of variance monster HP currently has, monster HP is now computed by this formula: (HD)d4 + HD\*2\*(size), where size is 0 for MZ_TINY, 1 for MZ_SMALL, and so on.
New msgtype intended to be even stronger than msgtype:stop, perhaps called msgtype:paranoid. Requires the user to type “yes” before continuing.
Note: A patch has since been created for msgtype:alert, which forces you to hit tab before continuing.
Make the Ranger quest artifact a crossbow if you are a gnome.
