Can you play Hextech Ray on an opponent's unit with Deflect if you only have 1 red rune available (not enough to pay the Deflect cost)?

Ruling: You cannot play Hextech Ray if you cannot pay the Deflect cost. Since Deflect is an additional cost that must be paid when targeting, and you need to target before finalizing the cast, you cannot legally play the spell if you lack sufficient resources.

Sequence:

• Pay the base cost to cast the spell
• Choose targets
• Pay costs to target (including Deflect)
• All associated costs must be paid before finalizing the play

Nuances:

• If a unit gains Deflect after you've already targeted it (e.g., through a chain buff), you do not need to pay the Deflect cost retroactively
• Deflect costs are paid at targeting and do not work retroactively
• If you attempt to make an illegal play at a tournament (targeting a Deflect unit without sufficient resources), it would likely be ruled a general error with a warning and rewind