I picked up these rules online and adapted them to 5th ed, simplifying some things here and there. I like to keep players on their toes and make them think twice before jumping into the fray. I also like how Constitution becomes an important score in combat and how easy this system is to implement with minimal change.

What do you think? I have left a couple of questions in line.

Anyone tried this already? I know there's an UA article on this but it's completely different.

Wound Points (WP)

The wound point system was developed as a more cinematic method of handling damage than the traditional hit point system. It aims at maximum compatibility with the currect system.  The system allows creatures to improve the amount of punishment they can withstand as they go up in level, while still allowing for a single lucky attack to take down any creature.

Characters using this system should be more wary in combat. This variant is an ideal system for low-magic campaigns or games where healing is otherwise rare. A very weak character in this system tends to be tougher to kill than in a standard game, since its Constitution score is often higher than the number of hit points it might have had. Very big creatures are also more durable, due to their size modifier, and tiny creatures are more fragile.  

Creatures capable of dealing a large amount of damage on a single hit become significantly more deadly in this system, since a lucky attack roll can give a deadly blow to almost any creature.

Constitution damage is especially deadly under this variant, since every point of Constitution damage reduces wound points by 1. If a creature’s Constitution is reduced to 0, it dies even if he has wound points remaining.  

Wound points measure how much true physical damage a creature can withstand, contrary to hit points which measure a creature’s ability to turn a direct hit into a graze or a glancing blow with no serious consequences.

A creature has a number of wound points equal to his current Constitution score multiplied by size, with a minimum of one.

Or:

Creatures without Constitution Scores

If a creature has no Constitution score, it has no hit points. Instead, it has wound points equal to the number of hit points it would have, multiplied by size. Such creatures are never exhausted or stunned by wound damage.

Or: Creatures with no Constitution score have wound points equal to the number of hit dice. Such creatures are never exhausted or stunned by wound damage.

Critical Hits

A critical hit deals the same amount of damage as a normal hit but that damage is deducted from wound points rather than from hit points. Critical hits do not deal extra damage, unless specified by a special ability, like Brutal Critical.

Creatures capable of dealing a large amount of damage on a single hit become significantly more deadly in this system, since a lucky attack roll can give a deadly blow to almost any character. I don't mind that as this is what keeps combat exciting and unpredictable. For criticals hits, consider reducing the additional damage from bonus damage dice (such as a flaming sword or a rogue’s sneak attack) to only 1 point per die. Or apply bonus damage dice to HP and weapon damage to WP?

Injury And Death

0 Hit Points

A creature who drops to 0 hit points does not start dying. Instead it allocates further damage to wound points.  

Taking Wound Damage

Wound points are reduced:

• from damage after hit points are reduced to 0,
• from damage when a creature is struck by a critical hit,
• from Falling; a creature suffers 1 wound point for every 1d6 of blunt damage taken by Falling,
• from Suffocating; when hit points from Suffocating drop to 0, wound points also drop to 0.

The first time a creature takes wound damage - even a single point - he suffers one level of exhaustion. Additional wound points damage doesn’t make the creature more exhausted.

In addition, any time an attack deals wound damage to a creature, he must succeed on a Constitution saving thow DC 15 or be stunned for 1 round.  Or: Delete stunned condition for simplicity.

Wound points cannot drop below 0; any damage that would cause a character’s wound point total to drop below 0 simply causes the creature to have 0 wound points.

0 Wound Points

A creature who drops to 0 wound points:

• starts dying,
• suffers one level of exhaustion,
• suffers one level of exhaustion whenever it fails a death saving throw.

Healing

Natural Healing

At the end of a long rest, a creature recovers 1 wound point and one level of exhaustion in addition to healing hit points. Any significant interruption during the rest period prevents the creature from recovering that night. A creature’s wound points can’t exceed its wound points maximum.  

Magical Healing

A creature recovers 1 wound point per spell level through magical healing in addition to the spell’s effect.

Greater Restoration reduces the target’s exhaustion level by one.

Special Conditions

Damage Reduction

Damage Reduction reduces damage dealt to wound points but not to hit points.

Regeneration

Regeneration applies to hit points as described in the standard rules and does not impact wound points.

Ok, I think I understand...

So a medium monster with 18HP and Con of 12, would have 18hp and 12 wp, and they would lose hp as they are attacked, and when this goes to 0 they switch over to wp. wp regenerates much slower so once you hit wp then you will want to rethink your being in combat.

Is that about the gist of it?

That's right.

Critical hits, falling and suffocation also deal damage directly to WP instead of HP.

D20 star wars worked that way and it was great. It also had damage reduction for armor instead of AC, that would take some work to incorporate in dnd (like what adds to DR and what adds to AC: loight/medium/heavy armor, mage armor, draconic bloodline, shield, shield spell...?). Anyway, it made much more sense and was very easy to use. I think dnd went too far with oversimplifying some aspects of the game, especially healing and dying. One moment you're dying, 6 seconds later you're running around like nothing happened. Ridiculous. Combat with wound points is much more thrilling. You never know how long you'll last.

For critical hits, consider reducing the additional damage from bonus damage dice (such as a flaming sword or a rogue’s sneak attack) to only 1 point per die. Or apply bonus damage dice to HP and weapon damage to WP ?

Isnt dnd supposed to be modular?

Havent you noticed how every book encourages you to adapt the game to your own taste?

Are you one of those very rare dm's who plays everything by the book?

Before you scream heresy! do you realise that other d20 games (dnd clones) have incorporated exactly this sort of wound point systems?

You seem to miss the point.  The point is not to make a life simulator but to make the game more fun. And this makes it fun to me. 

Quote from Lyxen >>

Honestly, this is because D&D has never meant to be realistic, and because you don't understand what D&D has been made to simulate, which is High Fantasy in which it is normal for people to run around like heroes can actually be running around collecting scrapes and burns and falling over the next second, and then running around some more because it's fun and heroic. This system, like all others of its kind just over-complicates things without making them more realistic because the impact of doubling the type of hit points implies taking into account all the possible sources of damage and assessing which one it would actually be targeting. possibly splitting things up.  And you end up asking questions like the one at the end which will generate rules that are, in the end, and when you consider all the possible spells and effects just bog down the game. And in the end, it will still not be realistic.

For me, this goes against all the DNA of D&D from the very first edition and against th streamlining of 5e in particular. So I would never use it, and the only thing I can say is that you are going to spend hours designing if and probably still be disappointed by its lack of realism.

 Just because you don't agree with them doesn't mean you have to be rude. They wanted to know whether people had played or wanted to play using this system, not whether some random person on internet thinks it's a waste of time.

I personally would not use this. The complexity reduces the modularity because it impacts more than one system of the game (constitution, creature sizes, new HP type, types of healing, etc.), without adding much depth. Thus making it more along the lines of a stand-alone mod where other smaller mods might require fixing if they were to be used in conjunction with it.

Your beginning goal of " I like to keep players on their toes and make them think twice before jumping into the fray" is probably where you want to restart at. There are simpler methods to do this. A common way is to add 1 point of exhaustion after a player character reaches 0 hp. This alleviates the tracking that needs to be done by the DM/PC as it doesn't create a new statistic in the first place. Nor does it have the DM be concerned about more stats on a creature that would need to be modified before hand.

The only other thing I have made that might be along the lines of risky combat is adding another condition so it can be used or not used without worrying too much about game system conflicts. Example: Deep wound - Prevents healing by hit dice. This is removed by receiving healing from other sources or spells like Lesser/Greater Restoration.

The DM can decide when and where that condition is applied (e.g. on critical hits, a trap, some spells or not at all). In lower fantasy games I presume it would be harder to get access to any type of healing so such a condition could be deadly. The DM can also decide that maybe after 7 long rests the deep wound "heals" over thereby removing the condition naturally.

Agree with Bumpkins on this.  if the idea is to keep players on their toes, some way of incorporating "deep wounds" is more appropriate.  In one of my groups, these happened on critical hits, or possibly critical failures on Acrobatics or Athletic checks.  Instead of unhealable wounds, we played it as broken bones or some such and imposed penalties like "no more multiple attacks" or "speed is reduced to 5" or just disadvantage on all physical skill checks, saving throws, and attack rolls, until the wound is healed by magic (like a Restoration spell) or extended time with Medicine checks.

On the other hand, the Ars Magica game does not use hit points at all.  When someone is hit they suffer a wound penalty.  A light wound exacts a -1 penalty, medium is -3, and heavy is -5, and then there is an incapacitating wound.  The penalties stack and apply to attack and defense rolls.  The damage amount is the difference between the attack and defense rolls, modified by the type of weapon and armor.  With this system, if someone has taken several wounds, the next hit that would otherwise be a light wound becomes a heavy or incapacitating wound because of the penalties to the defense roll.  Mind you, healing in Ars Magica takes a looong time, and magical healing requires some serious outlay of resources.  I'm not sure how this would port over to D&D, since there is no defense roll, but I know it's been discussed.  You might check out the Ars Magica forums on the Atlas Games website.

Several members of my gaming group are members of the Society for Creative Anachronism, and actually have mock battles (with armor and padded weapons).  These folks have always been upset by the way combat happens in D&D, because it is not at all realistic.  We've played around with all sorts of modifications, but keep coming back to just following the RAW with those deep wounds on critical hits for flavor, because it is simple and keeps the game moving.

Funny enough, this system was exactly what i were looking for an adaptation, an "hack" if you say, for an RWBY game.
Where Hitpoints serves as the Aura, and this Wound would be perfect.
Of course i would have to add an base "Regeneration" for everyone that has their aura awakened.