While one may be excused to consider HP as a sort of pool that represents how much life is left in you, this isn't actually the case. When a character takes normal HP damage, this represents your standard bruises, minor burns, cuts and contusions, and other damage that is largely superficial, with depleted HP representing physical exhaustion. Since MSF High is a place where you can't die by normal means, this is usually all that you need to deal with, but situations may dictate that more realistic damage needs to be taken account for. To represent more serious forms of damage, you may use the traumatic damage system described below. You may choose to make this system optional, in which case any rules that take advantage of this system may be given a non-traumatic alternative.
Traumatic Damage, also referred to as wounds, is damage to characters that goes beyond the standard bumps and bruises that normal damage represents. To determine whether a character has taken traumatic damage, you must know their Traumatic Damage threshold. This is equal to the character's defense plus half their threat level, rounded up. Thus, a level 5 character with an 8 defense would have a traumatic damage threshold of (8+(5/2)) 11. Any damage from a single source(such as one attack, one spell, one fall, or so on) that exceeds the character's traumatic damage threshold after soak is applied deals traumatic damage or some sort. An exhausted(0 to -def HP or 0 to -Int MP) character's traumatic damage threshold is reduced to their defense score. An unconscious(less than -Def HP or -Int MP) character's traumatic damage threshold is reduced to half their defense score, rounded down.
Now, determine the severity of the wound. By default, an instance of traumatic damage is considered severity 1, but for each time the amount of damage exceeds the threshold again, it is increased by 1. With the example above, 11-22 damage would be 1 severity, 23-33 damage would be 2 severity, 34-44 damage would be 3 severity, and so on. The severity of traumatic damage determines how profound its lasting effects are and how long it takes wounds to heal.
Next, we must determine where the traumatic damage is dealt. In the case of some damage sources, such as an accurate attack that targets a specific part of that character, the traumatic damage is dealt to that part of the character. In cases where it would make sense for the damage to be dealt to a specific location(like an item being held in a hand dealing its damage to the appropriate arm, or a hazard on the ground dealing damage to the feet, in which case roll do see which foot takes the damage)Otherwise, roll a d20. If the damage is from an attack made by a character of a different size, apply the difference between the damaged character and the attacker's sizes to the roll.
Feet/Legs: Damage to feet or legs keeps a character from moving properly. A character with wounds to their legs or feet takes a penalty to their agility rolls equal to their highest severity wound on any of those parts when that stat is used to move the character. This includes the character's dodge rolls.
Arms: Wounds on a character's arms make it more difficult to use whatever they're holding in those arms. Take a penalty equal to the highest wound severity level on an arm to any actions that use that arm's hand. If an action uses both hands, use the higher wound penalty there, too.
Torso/Shoulders: A wounded back makes it harder for a character to carry things. The character's strength is considered the highest wound severity lower for the purposes of strength to determine how much they can push or carry.
Neck: A wounded neck makes it harder for a character to talk. Reduce all social rolls that involve the character speaking by the highest severity of a wound on their neck.
Eyes: Damage to the eyes makes it difficult for a character to see. Reduce all rolls made that involve vision by the character's highest wound severity level to their eyes.
Head: Brain damage is no joke, and wounds to the head make it harder for someone to function overall. Reduce all rolls that use intelligence, accuracy, or personality by the level of their highest head wound's severity.
Next, we need to determine the sort of traumatic injury that is afflicted. Slashy, Pokey, and Ranged Projectile weapons usually do piercing wounds, while Smashy, Smacky, Punchy, Ranged Throwing, and Magical damage cause bruising wounds. Tangly weapons roll a d6, on an even roll they do piercing wounds and on an odd roll they do bruising wounds. Certain abilities or enhancements can alter this, and the GM may make a judgement call if it's unclear what sort of damage should be done.
Piercing: A pierced body part bleeds externally, and must be patched to keep it from bleeding. While bleeding, the target loses an amount of HP per round equal to the wound's severity. Spells and abilities that restore HP lower the amount of HP lost each round by 1 for every 10 HP healed, but if the target takes another piercing wound in the same location any other patched-up wounds will re-open back to their severity level. All piercing wounds' severity levels drop by 1 every time the character makes a successful self-healing check. If a character takes a severity 5 or higher piercing wound to any body part other than the torso or a 7 or higher severity wound to the torso, that body part is cut off completely or otherwise disabled and is unusable unless reattached by a skilled doctor or healing magics. A removed torso, head, neck, or shoulders kills the character instantly. The character will need to be reassembled before they can be brought back to life.
Bruising: A bruised body part may seem less damaged than a pierced body part, but it has effects that can be just as bad. A bruised character takes the total of their bruises' severities in extra damage whenever any source deals damage to them. Bruises stack on each body part, and if any body part other than the torso's bruise total reaches 10 or if the torso's bruise total reaches 15, that body part is completely crushed and is unusable until it is properly rebuilt and healed. A crushed torso, head, neck, or shoulders kills the character instantly. All bruises' severity levels drop by 1 every time the character makes a successful self-healing check.
Self-Healing checks: Once per day, a character who has gotten a full night's sleep(or however much rest they require) may make a single self-healing check. This is a difficulty 5 roll, and it is made as a non-skilled Defense roll. If a character gets a full day of bed rest, they can make a second self-healing check. A successful Self-Healing check will reduce all current traumatic damages by one level. Certain abilities or skills can lower this difficulty, and certain spells or abilities can increase the frequency of these checks.