Sunscour

• WWizards of the Coast2006-07-15
  Official Ruling
  You may pay the alternative cost rather than the card’s mana cost. Any additional costs are paid as normal.
• WWizards of the Coast2006-07-15
  Official Ruling
  You can’t exile a card from your hand to pay for itself. At the time you would pay costs, that card is on the stack, not in your hand.
• WWizards of the Coast2006-07-15
  Official Ruling
  If you don’t have two cards of the right color in your hand, you can’t choose to cast the spell using the alternative cost.
• WWizards of the Coast2006-07-15
  Official Ruling
  Paying the alternative cost doesn’t change when you can cast the spell. A creature spell you cast this way, for example, can still only be cast during your main phase while the stack is empty.

Rulings via Scryfall