When you are in a polyform with a hug attack and attack a monster with it, there is a chance the monster appreciates the hug and becomes peaceful.
When spells are forgotten or retention is damaged when you suffer amnesia, the game prints a message informing you of such, akin to “You forget some of your training” for skills.
Stairs should show any annotation of the level they lead to. Probably not by default, instead when using the nearlook and/or farlook command.
E.g. “There is a staircase down to level 2 (MUMAK BY THE STAIRS!!) here.”
A paranoid cannibalism option, which prompts you to confirm when you are about to eat something that would be considered cannibalism (including dogs and cats if they would incur the same penalties).
“Saintly” conduct, which tracks that you have never abused your alignment.
When you are riding and get engulfed, you should be “ripped from your mount”, because currently this behaves weirdly - you end up still riding your mount inside the engulfer, your steed is not adversely affected, and if you dismount you “float down” and the steed magically pops outside the engulfer. The size of your steed also doesn’t matter, so it also doesn’t make much sense if it’s something huge like a dragon.
Gray philosopher’s stone; a randomized gray stone that turns objects (possibly only of a certain material) rubbed on it into gold if non-cursed, and turns gold objects rubbed on it back into that same material if cursed.
Spell staves should remove a much greater share of armor penalties for spells of their associated school than they currently do.
Another possible bonus they could have to make them more worthwhile is to treat any spell of their associated school as cast at one higher skill level than your current skill in it (does nothing if you are already Expert, since defining Master effects for spells is likely out of scope).
Some ways to scale some spell effects with skill. Generally, this consists of nerfing unskilled and basic casting rather than adding even more powerful high-skill effects.
Using a spell staff allows you to cast spells of the associated school while not necessarily being able to speak (due to polyform or some other reason); it could also potentially suppress other impediments to spellcasting, such as confusion.
A silence spell for either players or monsters or both. Not specified whether it would be area-of-effect or targeted at specific creatures. The main function of silence effects would be to prevent spellcasting. Not specified whether this would also affect reading scrolls (though probably not since you can “cogitate” the formula on scrolls if polymorphed into a speechless form).
However, this may require defining certain existing spells as not requiring speech, because it does not seem entirely fair to take away all of someone’s escape or healing spells with fairly low level magic.
