Fiend Roar Deity Deineira

DT08-JP0(??)
Demon Roar God Deineira
LIGHT/Fiend
Level 8 - Effect
ATK: 2800 DEF: 100

You can Tribute 1 "Fiend Roar Diety" Monster to Tribute Summon this card in face-up Attack Position. While you control this face-up card, the effects of Normal Spell Cards activated by your opponent become "Your opponent selects 1 card in their hand and discards it". This effect can only be used once per turn.

question can you choose where would you activate this card or its mandatory when your opponent activate a normal spell card will this trigger

You can choose which spell card to use this effect on as long as your opponent uses a spell card, you can choose to use it or not...

thanks