Is Leona's "When I attack" ability mandatory, and must you pay the deflect cost even if the target unit is already stunned?

Ruling: Yes, Leona's "When I attack" ability is mandatory if you have the resources to pay for it (one rune). You must use it when attacking if you can pay the cost.

Nuances:

• The ability does not say "may" so it is not optional
• You must pay deflect costs when triggering the ability, even if targeting a unit that is already stunned
• A unit cannot be stunned twice, but this does not make the ability optional or avoid deflect costs