Shadowbound: "Embrace the Shadows and become invulnerable to death for 4-5 turns." This means that you can be at 0HP and not die until Shadowbound wears off.
Load any save where MC has Shadowbound. Open the menu, go to Skills, go to Magic, use Shadowbound. You'll see the Shadowbound icon show up next to MC's face. The icon will have a number telling you how many turns it will last.
Start a battle, any battle. You'll see that icon next to your HP meter. Surrender on your 1st turn. This will drop you to 0HP and fill your Adrenaline meter but you will not die. If you die, your game is bugged. Reinstall it. At the end of the turn, the Shadowbound icon's number will go down by 1. If you do nothing but Guard for the rest of the battle, you should not die while the Shadowbound icon is still there. If you die, your game is bugged. Reinstall it. At the end of the turn when the Shadowbound icon number is 1, the Shadowbound icon disappears and you die. If you don't want to die, heal yourself or use Shadowbound again.
All the icons for effects that wear off have a number telling you how long they will last. In battle, you'll only be able to see 2 icons, no matter how many effects MC has on him. You'll have to keep count for yourself.