What does everyone think about a proper heart rate mechanic?
Not just a stamina bar, but an actual heart rate system running in the background that affects different parts of gameplay. Sprinting, fighting, getting injured, being in a police chase or even certain mission situations could raise it. If the cocaine mechanic is usable in free roam, that could temporarily boost stamina/energy but also spike your heart rate, increase weapon sway, affect breathing etc. It could work the other way too, with resting or certain drugs lowering it, and maybe high stress affecting aim, recovery or how quickly stamina drains. Basically one underlying stat influencing