Antlion, an a-class monster which has a strong bite, has a holding attack, can hide on sand terrain, and can “drown” you by dragging you into the sand.

Strangulation protects you from drowning, since you cannot inhale water if you can’t inhale at all. It also prevents potion vapor inhalation effects and the inhalation effects of gas clouds. Basically it works like magical breathing except you die in 6 turns.

If a pet drowns while not in view, the game gives a special message: “You have a sinking feeling for a moment, then it passes.”

If you fall into water with teleport-at-will, the game should use casting a teleport spell as its last resort, once you have no other options for escape. It’s very annoying to attempt to teleport and lose energy and nutrition when you’re deliberately trying to jump in the water and can easily climb right back out.

Change how drowning attacks work, by making them pull you into a water square that is adjacent to both you and the attacker, and then sticking to you so you can’t move out of the water. This requires that the hero be allowed to survive (with a suffocation timer) underwater for several turns without magical breathing. If there are no mutually adjacent water squares, the attacker can’t use their drowning attack (it would either do nothing or you’d still be held but not get pulled anywhere). Unlike regular drowning, this wets your items each turn.

Give a YAFM if you would “sink like a rock” while currently turning to stone, or polymorphed into a stone monster (gargoyles, earth elemental, stone golem).

• if petrifying: “You sink like a rock, because you are becoming one.”
• if a stone monster: “You sink like a rock, because you are one.”

Attempts to analyze good instadeaths versus bad instadeaths (loosely defined as ones that are instant hard-to-avoid deaths that aren’t really similar to running out of HP):

• Poison, digestion, lava, death magic, and drawbridge instadeaths could easily be converted into HP damage of max(damage dice roll, substantial % of your max HP).
• Drowning and choking would be well-suited to a breath system, where it becomes a delayed instadeath. Especially so if you can stop the clock by putting on an amulet of magical breathing or praying.
• Intelligence drain and level drain generally can’t happen without the player being given ample time to escape, so they are fine.
• Starvation could be changed to HP loss, but you usually just die from side effects of fainting anyway.
• Instadeaths that almost always have to be intentionally caused by the player (self-genocide, divine wrath etc) are generally fine as-is.
• Instakilling artifacts are problematic, because there is currently no recourse except for the amulet of life saving.
• Eating or digesting the Riders should not instakill without warning, because it is now unexpectedly a bad idea to eat a reviving corpse, whereas it had been a good idea in the rest of the game.
• Good instadeaths generally use unusual resources to fix, or hit the player’s reserves in an unexpected way, and allow the player a chance to get out or stop it before dying.

The water walking property should protect inventory from water and protect against drowning attacks.