Artifact bronze plate mail The Pact Eternal. Autocurses when worn. When invoked, it summons a tame copy of you, with copies of your armor and wielded weapon (which only works on a wielded weapon), drains 1 level from you, and reduces your maximum HP by half.

If you die while the summoned copy lives, you get lifesaved, the max HP penalty becomes permanent, the copy is unsummoned and you are relocated in its place (to produce an overall effect of it becoming the “real” you.)

If you take off the armor, the copy is unsummoned.

If the copy dies or gets unsummoned by any means, its gear vanishes along with it, and your missing max HP is restored (though your current HP does not get restored).

Add two new elemental planes, those of Positive Energy and Negative Energy.

The Plane of Positive Energy:

• The full level is lit.
• Has lots of yellow lights, trees, and whatever plant-based monsters exist in the game.
• Everything is treated as if it has regeneration. The player can regenerate current HP past its maximum, but if this gets too far past the maximum, they instantly die from being unable to contain the energy (there are warning messages to this effect as you approach this point).
• Items in the player’s and monsters’ inventories can randomly get blessed, enchanted, or charged - even if this runs the risk of overenchanting and destroying them.
• Eating any food restores HP as well as nutrition.
• All exercisable attributes are exercised at regular intervals.
• All sleep effects are negated.

The Plane of Negative Energy:

• The full level is dark.
• Contains lots of undead.
• Everything constantly loses hit points. If you have regeneration, it either nullifies or only partly nullifies this effect.
• Items in the player’s and monsters’ inventories can randomly get cursed or lose enchantment or charges (going negative on things which are capable of being negative).
• You lose several times as much nutrition per turn as normal.
• All abusable attributes are abused at regular intervals.

A formula to provide diminishing returns on the HP growth you get from potions, which is currently unbounded.

In the formula, X represents the total amount of extra HP points you would have in vanilla (1 per blessed healing, 5 per blessed extra healing, etc), R represents the actual amount of extra HP points you will have under this formula, e is Euler’s number (a constant), and A represents the desired asymptotic upper bound of extra HP points you will approach:

R = (2A / (1 + e^(-2x/A))) - A

The value of A is up to the designer. If it’s selected as 100, for instance, total HP gains from potions will get closer and closer to 100 as more and more potions are consumed, but the hero will never quite reach it.

Iron golems rust in multiple stages, like iron items, rather than all at once. Each stage cuts its maximum HP by 20 (so a rusty golem has 60 max HP, etc.) Applying a can of grease will remove the rust and restore its max HP to normal, and may prevent further water damage for a little while. The golem may also quaff a potion of oil, which has a similar effect, except it also restores current HP as well as maximum by the amount of erosion removed.

Iron golems that rust to death may rarely leave behind a statue (ideally made of iron material) which is implied to be its rusted husk.

Set the upper bound for the upper limit of nurse dancing at 3 times the amount of maximum HP you had when you first gained your current experience level (which is saved by the game in versions 3.6 and later), instead of having it be a flat 25 times your experience level. This is to remove the rubber-band effect where roles that naturally have less HP can mostly catch up to roles that have a lot of it.

“The Amulet of Vitality”, an amulet of drain resistance that provides poison resistance and hungerless regeneration when worn and also increases your HP maximum by 20%.

Note: this could be implemented in a game that doesn’t have the amulet of drain resistance by instead making its base item the amulet versus poison and giving it drain resistance when worn.

The drain life spell heals you with some of the HP you drained from your target, possibly even increasing maximum HP by one point if it is full (though this is probably too powerful).

The healing isn’t intended for anyone who can cast it; it would require you to have a certain amount of attack skill and possibly be chaotic.

Don’t allow any single source of HP loss to kill you if you had full HP before the loss, unless your maximum HP is less than 10. (It would presumably leave you at 1 HP).

If a monster with an associated glob comes into contact with it (by moving onto it, or if someone hits it with the glob) it absorbs the glob and heals HP proportional to the glob’s weight. If this would heal it beyond its max HP, it gains a point of max HP.

Make it so that dying in a polyform carries a severe, possibly permanent penalty, such as losing some Constitution, maximum HP, or forcing you to a low percentage of current HP regardless of what you had when you first polymorphed.

Assuming a compound maximum HP system with a “miscellaneous bonus/penalty” factor (like the one described in #392) is implemented, make it a major trouble for prayer if this miscellaneous factor is deeply negative (e.g. -20 or below).

Being strangled for more than a couple turns starts to reduce your Constitution (or maxHP).

Track your maximum reached HP and Pw (or maximum “external sources” HP and Pw if using a system where it mainly depends on a stat and XL) and allow restore ability to also fix these.

Increase starting HP for all characters by some constant amount.

Scroll that restores you to full health but decreases your maximum health.

Temporary hit points and Pw: your maximum goes above its normal bounds for some time, before returning to normal. If your normal maximum changes for some reason, the temporary maximum changes by the same amount. There are two proposals for how the effect should end:

• The entire effect is timed, and once it ends the temporary buffer vanishes. If your HP would go below 1 as a result of this, you could either die or have it set to 1, depending on implementation.
• The temporary buffer drains away at the rate of 1 point per turn, and the effect naturally ends once it’s gone.

Healing potions don’t give you different HP maximum increases depending on their beatitude any more. Instead, if they would have taken you above your maximum, your HP maximum is increased by that amount, to a maximum of +1 (healing) / +2 (extra healing) / +4 (full healing).

Maximum HP depends totally on three factors: function(role, race, XL) + function2(XL, Con) + (all bonuses or penalties from other sources, like nurses, full healing potions, fire traps, etc), with some diminishing returns on the third factor.

Maximum HP should have some ceiling that depends on your race/role combination, proportional to what you would get by leveling up to 30 as that race/role.