Whenever I’m asked about cost reductions/increases, especially in the flurry of questions about it thanks to a newly spoiled card from the Izzet vs. Golgari decks, a joke I like to use is ʺApply increases, then reductions, then Trinisphere.ʺ
Trinisphere is really the only card that does what it does, and it seems to be a lot more confusing to some people at first glance than it really is. Basically, after you determine how much the spell costs thanks to the cost you elect to pay, and any additional/optional costs, you apply any increases [like Thalia, Guardian of Thraben or Grand Arbiter Augustin IV], then decreases [Herald of War or Etherium Sculptor], then Trinisphere if you would be paying less than 3 mana.
So say you cast Gut Shot in a non-red deck; you’d be paying 2 life and no mana. With a Trinisphere out, you have to pay 2 life and 3 mana instead. The life you pay for a phyrexian mana symbol is not actually mana, so Trinisphere pays no attention and says “3 mana please!” Ditto for Gitaxian Probe or Mental Misstep. And if you want to play Dismember, you’re either paying 1BB, 2B and 2 life, or 3 mana and 4 life.
Today’s Rules Tip written by
Trevor Nuñez, Level 1 judge from Roswell, NM