Spells you cast cost less to cast for each card with the same name as that spell in your graveyard.
Locket of Yesterdays reduces only the amount of mana you need to pay to cast a spell. The spell’s mana cost and mana value are not affected.
Colored costs can’t be reduced by this effect. For example, a spell that costs can’t be reduced by more than .
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.
can’t be reduced by more than