Stamina is a game mechanic in Demon's Souls.
In general, it is a measure of a character's ability to physically exert him/herself without tiring. Making certain actions decreases stamina, which can be monitored via the green bar below the player's Health and Mana bars on the HUD. Enemies capable of blocking also have a hidden stamina gauge, which functions exactly like the player's. The player's stamina can be increased by leveling up Endurance.
The following actions will subtract from the player's current stamina:
- Punching/physically attacking with a weapon and missing, hitting, or being blocked
- Physically attacking with a weapon and hitting a wall or unbreakable object (takes more stamina than normal attack)
- Attempting to perform an evasive roll (same cost regardless of success or failure)
- Headbutting/pushing with a weapon (less cost than a normal attack)
- Absorbing an attack by blocking (depends on weight of blocked attack; player will be staggered for a moment if stamina cost to block an attack is greater than his/her remaining stamina)
If the player's stamina is zero or less, the player will be unable to perform any action that costs stamina until stamina regenerates back to at least one point. Wearing the Eternal Warrior's Ring increases the rate at which stamina regenerates; wearing heavy armor (weighing as much as Fluted Armor or heavier) or contracting the plague decreases the rate at which stamina regenerates.