||For the trinket with a similar name, see Found Soul. For another trinket with a similar name, see Your Soul.
Lost Soul is a passive item added in The Binding of Isaac: Repentance.
- Gives Isaac a small soul familiar that closely follows behind him. If the soul takes damage, it dies, respawning at the start of the next floor.
- If the soul survives to the start of the next floor, it spawns one of the following:
- Floors completed during the Ascent count.
- It is advised to skip picking up the item until after you clear the floor, in order to guarantee rewards.
- After the Mother's Shadow chase, the Lost Soul familiar will be revived allowing you to have a second chance at a reward.
- BFFS!: Gives the Lost Soul Holy Mantle.
- Forget Me Now: Restarting a floor triggers the Lost Soul if it is alive.
- Tainted Isaac: Swapping Lost Soul for another item and picking it back up again will cause it to respawn if it died previously.
- Bursting Sack Does not provide immunity to contact damage from spiders to the Lost Soul.
||If the Lost Soul is killed before the chasing with Mother's Shadow, it will respawn after you leave the place containing Knife Piece 2 safely.
||When playing as Tainted Lazarus, if Lost Soul is killed, it will respawn on the same floor it died on as soon as Tainted Lazarus flips again.
||Lost Soul can die if it touches projectiles generated by friendly enemies (spawned from Mystery Egg, for example).
||Lost Soul will give rewards when moving from the starting room of a floor to the previous floor with Glowing Hour Glass twice.