If a unit with Deflect gains additional Deflect from equipment (like Hexdrinker) via a reaction after an opponent plays a targeting spell (like Void Seeker), does the opponent have to pay the increased Deflect cost?

Ruling: For spells like Void Seeker that target on play, Deflect costs are determined and paid when the spell is played, before reactions can be used. Gaining additional Deflect after the spell is played does not change the cost already paid. However, for spells like Falling Star or Icathian Rain that create triggers which target on resolution, Deflect costs are checked when each trigger resolves, so gaining Deflect before resolution will increase the cost.

Sequence:

• Opponent plays a spell like Void Seeker and chooses targets
• Deflect costs are determined and paid at this time
• The spell goes on the chain
• Players can now play reactions
• If you equip Hexdrinker now, it does not affect the Deflect cost already paid for Void Seeker
• Any NEW spells or abilities played after Hexdrinker equips would need to pay the increased Deflect cost

Nuances:

• For spells like Falling Star and Icathian Rain, targets are chosen when each trigger resolves (not when the spell is played), so Deflect costs are checked at resolution
• If the opponent chooses not to pay a Deflect cost for a particular trigger of these multi-trigger spells, that trigger is removed from the chain immediately before any triggers resolve or other reactions can be played
• Multiple instances of Deflect do stack