Wizard of the Cost

If an opponent would put a nonland permanent onto the battlefield without paying its mana cost, they pay that nonland permanents mana cost plus an additional {2}. If they don't sacrifice that nonland permanent.

Opponents spells cost {2} more to cast.
Spells you cast cost {w/u} less to cast

Of course you should pay full price for things, and maybe some more to support the spell makers.