Here are my house rules on lingering injuries. I admit to the phrasing being a bit clumsy but it's just a house rule.
In case you think I only use a stick I also have a system for what I call "Peak condition benefits" which are things that a bit like inspiration or boons that a character can build up by spending time training or getting a blessing etc and are intrinsic to the character rather than linked to an item.
Enjoy
Lingering injuries
Every time you fail a death save roll or take a critical hit you have a chance of suffering a lingering injury. If you suffer the same number as your hit dice ( or biggest hit dice if you are multiclassed ) you automatically receive one lingering injury. Then the chance to suffer another one starts to build.
Whenever you take a long rest you roll a dice equal to your hit dice. If you roll equal or less than the chance of suffering a lingering injury you have one. After the long rest the chance of suffering a lingering injury them resets to 0.
(I.e. Bill the fighter suffered 3 critical hits and failed a death roll during the days fighting. He rests overnight and roll 1d10 ( his hit dice). If he rolls a 4 or less he wakes up with a lingering injury. If he had suffered say 12 critical hits and failed 5 death rolls he would suffer 1 lingering injury and have a 7 in 10 chance of suffering a second. If he had this happen to him and he was a monk or cleric he would have 2 lingering injuries and a 1 in 8 chance of a third )
Roll on the table below to see what injury lingers. You may suffer all except 1&8 multiple times. If you can no longer suffer the injury rolled, roll again.
Lingering injuries
1.Weakened: roll damage dice twice take the worst result.
2.Frail: hit point maximum reduced by 2 per hit dice/level
3.Scarred: disadvantage on skill checks of a particular stat (roll1d6)
4.Lame: lose 10' movement
5.Injured : take a few seconds to warm up. Disadvantage to everything for the first two rounds involved in each combat (including initiative).
6.Vulnerable: double damage from a particular damage type (GM choose one that caused the injury)
7.Feeble: disadvantage on saves of a particular type (roll 1d6)
8.Afflicted: hit points recovered from any source (healing, hit dice etc) the result is halved (round down)
Recovery from lingering injuries
You can recover from a lingering injury by making a DC 15 constitution save. After spending 3 weeks recuperating you roll. A person making a DC 15 intelligence (medicine) roll or casting a heal spell can give you advantage on this save. This time is reduced to 1 week if you have access to regular magical healing. After a success an injury resolves, you can only heal one at a time. A regenerate spell will heal all lingering injuries
Very cool. I like your list of effects. I may incorporate them as other options. My approach is quite similar, but I wanted to leverage existing 5e mechanics as much as possible, and also maintain the abstract approach that D&D combat uses.
We use a modified version of the exhaustion track. Injuries can occur because of a critical hit (if you fail a save) or are reduced to 0 hp (always). We have a similar condition called wounded that is like an encounter-level version of Injured. Again, you can be wounded due to a critical hit or when you reach 0 hp. Note that using the Condition Track at 0 hit points allows a creature to remain conscious longer, but has a much longer recovery time.
Note that for critical hits, the player chooses where they hit. Armor has an impact here. So if a creature is wearing a helm, they have advantage on saving throws that target that location, such as when they take a critical hit. They can, of course, go for the face, neck, whatever, but the DM determines if there's any modifier to the roll. Regardless, they have to fail by a significant amount for the effect to be serious.
The severity level of these is at the player's requests. We worked through the math to figure out what odds they wanted to survive if somebody didn't get any help, for example. While we've had a number of people wounded, we've only had a couple of injuries, and still only one death using these rules over the past 8 months or so. They respect the 0 hit point threshold much more, and naturally avoid it as much as possible. They like the idea that hit points account for skill, luck, and stamina. So they wanted something to measure your actual health. Using the condition track means you have a fixed amount of health, and the critical system allows you to bypass hit points and impact that health directly. One of our current discussions is whether we should expand that track to more than 6, especially in relation to Constitution bonuses. However, most of these saving throws are Constitution based, so better Constitutions are already accounted for.
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CRITICAL HITS
• You can score a critical hit with a weapon attack (including natural weapons), not spell attacks.
• You score a critical hit when you roll 5 or more needed to hit and a natural 20. Some abilities reduce this threshold to a 19 or 18.
• You cannot choose to reduce a critical hit once it has been rolled. Your attack is deadly, even if it’s unintended.
The effects of a critical hit are:
• Choose the hit location.
• Roll all damage dice twice then add modifiers.
• The creature must make a Strength, Dexterity or Constitution saving throw (whichever is better). If they fail, they suffer:
o One level of wounded.
o Fail by 5. They are incapacitated.
o Fail by 10. They are injured, stunned, or unconscious (DM’s choice).
o Fail by 15 and a Natural 1. Your attack is lethal. The creature is decapitated, has their skull crushed, a strike through the heart or other vital organ, etc. It need not be instantaneous, but only long enough for a dying breath.
• The effects are cumulative. The creature can make a Constitution saving throw at the end of each round to end any conditions other than injured, unconscious or dead.
CRITICAL MISSES
You score a critical miss when you roll a natural 1.
You decide the results. Some examples are:
• Attackers have advantage.
• You suffer a minor condition as the result of equipment failure, the environment, or your own ineptitude.
• Conditions can be blinded, deafened, debilitated, disarmed, knocked prone or kneeling, etc.
• You might accidentally strike an ally.
• You could slip and fall down the stairs you’re standing on, or the railing you’re leaning on breaks, or your sword blow missed and is now stuck in a table or support, or your bowstring breaks, or halberd shaft splits.
The results should be dramatic, meaningful and situational. They will almost always provoke an opportunity attack (assuming you missed by 5 or 10 more than needed to hit).
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CONDITION TRACK
Level Effect1
1 Disadvantage on all d20 rolls
2 Speed halved, and no reactions
3 Incapacitated, reduced to 50% of Maximum hp
4 Stunned
5 Unconscious and potential permanent effects
6 Death
Effects are cumulative.
1Specific conditions may have other effects.
WOUNDED (CONDITION TRACK)
You cannot recover hit points through non-magical means when you are wounded.
Saving Throw. Start of turn.
1 Success. Stabilized.
1 Failure. Worsen by one level.
Recovery: Heal 5 hp with magical or mundane healing to stabilize. Heal 5 hp with magical or mundane means to recover each level of wounded.
When regaining any level of wounded taken at 0 hp, make a Constitution saving throw, or suffer 1 level of injury. The DC is 15 + the worst level of wound taken.
INJURED (CONDITION TRACK)
Saving Throw. 24 hours.
3 Successes. Improve by one level.
3 Failures. Worsen by one level.
Level 5 imposes a permanent effect.
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DROPPING TO 0 HIT POINTS
When you drop to 0 hit points, you are wounded. Any hit against you causes one additional level of wounded for every 5 points of damage.
EXCESS DAMAGE
Excess damage can kill you instantly. When damage reduces you to 0 hit points you suffer an additional level of wounded if the remaining damage equals or exceeds ½ of your maximum hit points.
If the excess damage equals or exceeds your hit point maximum, you suffer four levels of wounded.
If the excess damage exceeds double your hit point maximum, you are killed instantly.
RECOVERY
When you recover from being dropped to 0 hit points, you suffer a level of injury equal to the worst level of wounded you reached while at 0 hit points.
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HEALING
MEDICINE SKILL
You can stabilize a creature (stop the saving throws) for wounded.
You can reduce the effects, but not the severity, of an injury by 1 step. This can only be done once per injury.
LESSER RESTORATION (2nd level spell)
You can reduce the effects, but not the severity, of an injury by 1 step. This can only be done once per injury.
RESTORATION (3rd level spell)
You alter the ratio for recovery of Injured (and Diseased) to 4 failures and 3 successes. The ratio can't be any greater than that.
GREATER RESTORATION (5th level spell)
Grants advantage on save to recover Injured or Diseased (still only one save per day).
REGENERATION (8th level spell)
Heals Injured or Diseased.
