Sunscour — ruling 1

You may pay the alternative cost rather than the card’s mana cost. Any additional costs are paid as normal.

Sunscour — ruling 2

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.

Sunscour — ruling 3

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.

Sunscour — ruling 4

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.

Sunscour : règles, fonctionnement et interactions (MTG)

Sunscour is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

You may exile two white cards from your hand rather than pay this spell's mana cost. Destroy all creatures.

How it works : Sunscour

Original English text — Wizards of the Coast / Scryfall

#1July 15, 2006· Wizards of the Coast
You may pay the alternative cost rather than the card’s mana cost. Any additional costs are paid as normal.
No other card is named in this ruling.
#2July 15, 2006· Wizards of the Coast
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.
No other card is named in this ruling.
#3July 15, 2006· Wizards of the Coast
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.
No other card is named in this ruling.
#4July 15, 2006· Wizards of the Coast
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.
No other card is named in this ruling.