HP

HP, or Hitpoints, or are an integer value which measures how close a creature is to death, or how intact items and walls are.

Losing and Gaining Hitpoints
Attacks which successfully hit their target and penetrate through any AV or MA which it may have will deal damage, reducing the hitpoint total of whatever is hit. Additionally, some effects, such as being on fire or bleeding, will continually decrease the hitpoints of those afflicted with them.

Certain items, such as or  will restore hitpoints over time. Other items, such as or  will restore hitpoints instantly.

Furthermore, many creatures will naturally regenerate a number of hitpoints each turn according to the following formula:

$$\frac{20 + 2 \times ( \text{Willpower Modifier} + \text{Toughness Modifier})}{100}$$

Taking damage interrupts natural HP regeneration for 5 turns, unless the creature has the Regeneration mutation, which prevents this effect. Those with the Regeneration mutation also gain a percentage boost based on the mutation's level to their natural HP regeneration.

Maximum Hitpoints
At character generation, the player character has a hitpoint maximum equal to their Toughness score. Each level after that, they will gain 1d4 + Toughness Modifier maximum hitpoints. This toughness modifier is retroactive, so if a level 12 character levels up to 13 and moves from a Toughness Modifier of +2 to +3, they will gain 1d4 + 12 hit points that level to make up for the 12 earlier levels where they did not have the +3 modifier.