Sacrifice is a non-canon, or fanon (a term for works that are canon only to the fans), ending in Ib: Green Edition. It involves Ib sacrificing her life in order for both Mary and Garry to survive.
The walkthrough is similar to Promise of Reunion's, except that Mary's painting shouldn't be burnt and, when Garry and Ib are about to return to the real world through the Fabricated World painting, Mary will run towards them yelling, "I'M NOT LETTING YOU LEAVE!!!!!" Garry will then say, "Ib! Don't!" before Mary gets impatient and starts to get upset, thinking Ib is leaving with Garry. Shortly, Mary will start to cry. Ib will, then, get the option to choose if she leaves with Mary, Garry, or to sacrifice her life to save them both. When choosing Mary, you will receive Together, Forever, and upon leaving with Garry you will get Memory's Crannies. After Ib becomes tired of having to choose and feels weak, she will decide to sacrifice her life and proceed to rip the petals off of her rose. Afterwards, the game will say, "You feel tired." Ib will then push Garry and Mary into the mural that Ib, Garry, and Mary were just standing in front of. Upon leaving the Fabricated World, Mary will start to complain saying that she doesn't feel well and wants to go home. When Mary sees the portrait of Ib, she will cry out, resounding "Ib...".