Locket of Yesterdays

Oracle Text

Spells you cast cost 1 less to cast for each card with the same name as that spell in your graveyard.

Card Rulings

9/25/2006 Locket of Yesterdays reduces only the amount of mana you need to pay to cast a spell. The spell’s mana cost and converted mana cost are not affected.
9/25/2006 Colored costs can’t be reduced by this effect. For example, a spell that costs can’t be reduced by more than .
9/25/2006 The spell being cast doesn’t reduce its own cost, even if you’re casting it from a graveyard. At the time the cost is reduced, the spell is on the stack.