The cool thing about Divine Mercy Sunday is . . . If you confess to a priest and receive Communion on this day, God not only will forgive you, he will also erase all the time in purgatory you owe up to that point (provided you are truly repentant and have no lingering attachments to sin, venial or mortal).
The Feast of Divine Mercy Sunday falls on the Sunday after Easter. Many parishes have special Divine Mercy Sunday Masses at 3 p.m. to commemorate the Lord's death at this time.
Jesus delivered the good news of this feast he wished to establish to St. Faustina when He appeared to her.