If you manage to avoid dying by sinking in lava by freezing it solid, you are stuck to the spot for a few turns and when you escape, you leave your boots behind (probably either destroyed, since they cannot be recovered from the solid stone, or buried, and recoverable by digging a pit on the spot).

You can tip a potion of levitation onto the ground, which in addition to its normal vapor effects, causes any objects buried there to float to the surface.

Not specified on if this would have an effect when over a liquid; perhaps the items would temporarily float to the surface and immediately sink back down.

Artifact chaotic helm Helm of the Underworld, modeled after Hades’ helm. Grants drain resistance, invisibility, magic resistance, and passive detection of buried objects (or phasing, if this is too difficult to implement) when worn. When invoked, it does a stronger version of the chaotic turn undead effect (rebuke or tame undead).

In regular dungeon levels, a certain engraving can occasionally generate which has treasure buried beneath it.

(Note: This idea predates the 3.7 themed room containing buried treasure and an engraving elsewhere on the level which points to it.)

You can bury fruit to make a tree grow where the fruit was buried.

Apply the digging-a-grave-up behavior (summoning undead, alignment penalties, etc) when a gravestone is kicked over, as well as digging it up. (The substitute for “You unearth a corpse” is to silently create a corpse buried under where the grave used to be.)

Trees’ fruit is generated along with the tree (possibly buried for code purposes so that it shows up on object detection but not when you just look at the tree, or perhaps just “embedded in the tree” is good enough). When you kick or chop down the tree, this fruit is released rather than generating some fruit on the spot.

Random piles of loot can sometimes generate buried in the floor or behind walls on spaces not adjoining any walkable spaces. Nearby engravings are generated to indicate that there is something in the vicinity. Archeologists get an alignment bonus for digging out these items.

If fossils exist, they should generate buried beneath gravestones.

The treasure found under randomly generated gravestones should be more treasure-like or the sort of items that get buried in graves in real life, rather than just random objects.

You can pray at a gravestone, or possibly ring a bell at one, to cause any of a number of good and bad effects:

• Summon a ghost, which might be hostile or peaceful.
• Summon a hostile undead, flavored as it forcing its way up out of the grave. Usually a zombie.
• Polymorph you into a zombie or mummy of your own race.
• Put you to sleep, ignoring resistance.
• Create a swarm of hostile manes or lemures.
• The headstone falls on your foot, dealing some damage, less if wearing boots (“killed by a falling tombstone” if fatal).
• If the grave is a bones pile grave, the ghost of the player always appears. It will be peaceful if their alignment matched your own and hostile otherwise.
• Various cosmetic messages that do nothing. “The air suddenly turns cold.” “The engraving on the headstone shimmers for a moment.” “A shiver runs down your spine.”
• The dirt cracks open and spits out any items buried under it.
• A voice from nowhere whispers a random rumor, true or false.
• The epitaph on the grave changes. This does not flag the grave.
• Get an alignment bonus for honoring the dead (this is only if triggered by praying). “You feel that the one buried here is content.” Bonus might be larger if you’re lawful or a Priest, probably 1 otherwise. This should possibly happen before and independently of any other effects.
• Limited identify of 1 item.
• Type-identify of multiple un-type-identified items in the inventory, but the player doesn’t get to pick which. Might pick 0 items (flavored as the spirit not knowing anything new about what the hero is carrying).
• Enlightenment.
• Temporary telepathy / sleep resistance / infravision / other intrinsic.
• The gravestone rumbles and moves aside, revealing a branch staircase to a just-created-now one-level branch, a small one-off “crypt” floating branch that contains some undead, some boxes containing corpses, and some treasure. This only happens on gravestones in the Dungeons of Doom.
• You “feel that the dead are restless”, aggravating monsters level-wide. All gravestones on the level become flagged against further attempts. This effect could be added to and independent of other ones, and if so, it’s a chance dependent on the number of already flagged gravestones on the level, which provides a nice way to balance it on levels that have massive amounts of gravestones.

After you get one effect, the gravestone is flagged so that it doesn’t happen again (or, more evilly, that any further attempts will only result in bad effects). Possibly shouldn’t work at all on graveyard levels, because they have too many graves to balance these effects.

When a black pudding is created from a sink, rings buried beneath the sink may be placed into the inventory of the pudding.

Spiked pits and a lower percentage of pits generate with an item or two buried. When you fall into one, any buried items are automatically exposed. The most commonly generated items here are a few gold or an eroded weapon.

All sinks spawn with a ring buried beneath them. If you kick the sink and get the “Flupp! Muddy water” message, the sink will spit out one of the rings buried under it. This removes the need for the S_LRING flag, and also allows players a non-destructive way to retrieve rings they dropped down the sink.

Throwing a cockatrice corpse into water turns it into a hard floor, or possibly ice, with the corpse buried in the new floor.