Morophon, the Boundless

• WWizards of the Coast2019-06-14
  Official Ruling
  If a spell has hybrid mana symbols in its mana cost, you choose which half you will be paying before determining the total cost. For example, if a spell of the chosen type costs , you may choose for the cost to be and then reduce it to .
• WWizards of the Coast2019-06-14
  Official Ruling
  Morophon's effect reduces the total cost by up to one mana of each color. For example, if a spell of the chosen type costs , it will cost after applying Morophon's effect.
• WWizards of the Coast2019-06-14
  Official Ruling
  You must choose an existing creature type, such as Sliver or Warrior. Card types such as artifact, and supertypes such as legendary or snow, can't be chosen.
• WWizards of the Coast2019-06-14
  Official Ruling
  Cost reduction effects are applied after other cost modifiers, so Morophon can reduce additional costs or alternative costs of spells of the chosen type.
• WWizards of the Coast2019-06-14
  Official Ruling
  Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to other creatures you control of the chosen type may become lethal if Morophon leaves the battlefield during that turn.

Rulings via Scryfall