Thalia, Guardian of Thraben

• WWizards of the Coast2018-03-16
  Official Ruling
  To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
• WWizards of the Coast2018-03-16
  Official Ruling
  Thalia's ability affects each spell that's not a creature spell, including your own.
• WWizards of the Coast2021-11-19
  Official Ruling
  To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
• WWizards of the Coast2021-11-19
  Official Ruling
  Thalia's ability affects each spell that's not a creature spell, including your own.

Rulings via Scryfall