Stamina represents your character ability to dodge, evade or otherwise avoid getting injured. The amount of Stamina you have is determined by your class and Dexterity modifier and you gain more as you level up.

Stamina can be used in certain ways. You cannot use Stamina when you have the Bloodied condition.

Stamina AbilityEffect
SidestepReaction. Trigger: You are hit by an attack. You spend 5 Stamina to turn a hit into a near miss. Reduce the damage of the triggering attack by a number of d6s equal to half your level + Dexterity modifier.
RollReaction. Trigger: You are targeted by an area of effect that allows a Dexterity saving throw. You spend 8 Stamina to dive clear. On a success you take no damage instead of half, and on a failure you take half damage instead of full.
Catch Your Breath1 Action. Frequency: Once per Turn. You spend a moment to collect yourself, recovering Stamina equal to your Dexterity modifier + your level.
Second WindFree Action. Frequency: Once per Turn. You spend 15 Stamina to push past your limits.

Note:

Not sure how I feel about Stamina being so dexterity dependent. Your total amount being tied to it is fine but its effectiveness being tied to the same attribute makes classes like rogue really powerful and Barbarian barely gets the use the system at all.

Currently the cost for using Stamina is very high at early levels but very small at higher levels. Half the abilities also use a reaction, which a lot of classes will probably have a better use for.

Sam Notes

modify catch your breath action to have variable action (1-3) have stamina be more useful outside of combat (skills and stuff) have martials have more options

Rule revision3