Can you choose to not play Deflect costs upon playing a spell, making it fizzle?
No, you cannot choose to not pay Deflect costs to make a spell "fizzle."
According to RiftJudge FAQ #6603 and Rule 809.1.d, the Deflect cost is a mandatory additional cost that must be paid during the finalization of the spell (when you declare the target). Because this cost is required to place the spell on the chain, you cannot choose to skip it. If you cannot pay the mandatory cost, you cannot play the spell targeting that unit in the first place.
Furthermore, as noted in RiftJudge FAQ #478, spells do not "fizzle" in Riftbound. If a spell is successfully played and placed on the chain, it will resolve normally even if the target later gains Deflect or becomes illegal for other reasons.
Summary of the Process:
- Finalization: When you play a spell that targets a unit with Deflect, you must declare the target and pay all costs, including the mandatory Deflect cost.
- Chain: Once the costs are paid and the target is declared, the spell is a legal item on the chain.
- Resolution: Because the cost was paid during finalization, the spell resolves normally. You cannot retroactively choose not to pay the cost to make the spell fail.