Upon death, Isaac turns into a ghost that is linked to Isaac's dead body, similarly to The Soul, and can continue fighting with 1/2 of a heart. Isaac comes back to life 10 seconds after this effect occurs if he doesn't take damage while in ghost form.
After this effect occurs, Spirit Shackles cannot activate again until Isaac gains a half or full Soul Heart or a Black Heart. Soul Hearts that are used to charge Spirit Shackles will not be added to Isaac's health.
When the Shackles are ready, their costume on Isaac's arms is light blue. When they are drained and cannot protect from death, they are gray.
The entire heart gained is used to charge the item, although only a half heart is required.
In the case of blended hearts, Spirit Shackles will only be recharged if the blended heart would give Isaac soul health.
If Spirit Shackles is uncharged, items that add soul hearts directly to Isaac’s health (such as Rosary, Cancer, or Book of Revelations) will recharge Spirit Shackles and give one less soul heart.
Isaac will have invulnerability frames for 1/3rd of a second after reviving, allowing him to get off of spikes he stepped on if they were what killed him.
Spirit Shackles can be recharged while it is active, but it cannot re-activate until its effect ends.
When Isaac returns to normal, he will be placed where his body was.
If Isaac leaves the room while in ghost form, he will not be chained to anything and can move freely. He will also come back to life at his current location rather than where his body was left.
Isaac can be trapped by this if he's in the middle of a pile of rocks when this happens. This can be fixed by save-quitting, then continuing the run.
If Isaac dies while in ghost form and is brought back to life by a respawn item, he will have flight and spectral tears until it would normally be removed.
Spirit Shackles cannot activate in the Mirrored World, nor can the ghost form given by it be used to enter the Mirrored World.
Spirit Shackles will trigger if a fatal Devil Deal is taken.
The Lost: Effectively acts as a rechargeable extra life, granting additional defensive measures on top of his inherent Holy Mantle and granting a use to normally useless Soul Hearts.
Magic Skin: When all hearts are converted to Broken Hearts, Isaac will be revived with half a soul heart, allowing many more uses with low health.
The Forgotten: Spirit Shackles can activate for both characters. They can toggle between The Forgotten and The Soul as normal while it's active, and the form that didn't "die" will have their normal health. Toggling from The Forgotten to The Soul will also create another body of The Forgotten that The Soul will be chained to in addition to the original body.
Jacob and Esau / Tainted Lazarus: The character that has Spirit Shackles must die for it to activate; if the other character dies, it will not activate. Only the character that has Spirit Shackles can recharge it.
In the case of Jacob and Esau, the brother that has Spirit Shackles will be chained to their dead body, while the one that doesn't can move freely. If either brother dies while Spirit Shackles is active, the other dies with them as normal.
Keeper / Tainted Keeper: Cannot be recharged by picking up soul hearts, as they are turned into blue flies while playing as them. Effects that would add soul hearts to health directly, however, can recharge it.
Tainted Forgotten: The ghost will spawn from Tainted Forgotten instead of Tainted Soul; it will be invulnerable, unable to move, and use the bone club instead of Tainted Forgotten. It can also be thrown, but will rapidly return to Tainted Forgotten due to being chained to them. Tainted Soul is unaffected, and can take damage as normal.
Tainted Jacob: Dark Esau will not activate Spirit Shackles if Tainted Jacob isn't already in his "lost" state. If he is, Spirit Shackles acts normally.
If Tainted Jacob's body is still in the room, Spirit Shackles will chain him to it when it activates.
If Dark Esau touches Tainted Jacob or dies while Spirit Shackles is activated, he will enter his "lost" state and drop an extra body. When Spirit Shackles' effect ends, he will return to life where Dark Esau turned him into his "lost" state and be chained to the original body until he leaves the room or the run is exited and resumed.