When Isaac's health is brought down to half a red heart and no soul hearts, a Little Steven familiar spawns for the current room.
When Isaac enters a room and has half a red heart or less, a Little Steven familiar spawns and will remain until red health is restored to above a Half Red Heart, disappearing after entering another room.
Characters which cannot acquire red heart containers in any way will always have a Little Steven.
When Isaac takes damage, there is a chance to spawn a Gemini familiar for the current room. This effect is stackable.
The chance to spawn the familiar depends on the luck stat, and the formula used to determine the chance is: .
At 0 luck the chance is 30%, maxing out at 100% at 35 luck.
When Isaac's health is brought down to half a red heart and no soul hearts, a 
Little Steven familiar spawns for the current room.
When Isaac enters a room and has half a red heart or less, a Little Steven familiar spawns and will remain until red health is restored to above a Half Red Heart, disappearing after entering another room.
Gemini familiar for the current room. This effect is stackable.
The Binding of Isaac: Rebirth
