Is Deflect considered part of a spell's cost, and can cost reductions (like Vex Cheerless's combat discount) apply to the Deflect cost?

Ruling: Deflect is a mandatory additional cost that becomes part of the total spell cost. Cost reductions like Vex Cheerless's discount apply after adding the Deflect cost, so they can reduce both the base cost and the Deflect cost.

Sequence:

• Start with the spell's base cost
• Add mandatory additional costs (including Deflect)
• Apply cost reductions and discounts
• Pay the final calculated cost

Nuances:

• Deflect is NOT optional when casting spells or using activated abilities - if you choose a unit with Deflect as a target, you must pay the Deflect cost
• The "may" option for declining to pay costs only applies to triggered abilities, not to spells or activated abilities
• Effects that don't target (like Ahri Legend's ability that applies effects based on conditions) do not trigger Deflect costs
• Ezreal's effect would not apply to Deflect costs (though the specific reason why is not detailed in the thread)