Can you decline to pay deflect costs, and if so, under what circumstances?

Ruling: You can decline to pay deflect costs, but only for triggered abilities. You do this by choosing not to put the trigger on the chain in the first place. You cannot decline to pay deflect costs for spells or activated abilities.

Sequence:

• When a triggered ability would target a unit with deflect, you choose whether to put that trigger on the chain
• If you choose not to put the trigger on the chain, you don't have to pay the deflect cost
• If you do put the trigger on the chain, you must pay the deflect cost

Nuances:

• This only applies to triggered abilities (like Leona's stun when attacking, or Icathian Rain's reflexive triggers)
• You cannot decline to pay deflect costs for spells (like Hextech Ray) or activated abilities (like Iron Ballista)
• This rule was added in version 1.1 of the rules