Precognitive Perception
Instant
Draw three cards.
Addendum — If you cast this spell during your main phase, instead scry 3, then draw three cards.
"To control the present we must master the future."
Chris Rallis
Rulings
Addendum abilities of instant spells apply while the spell is resolving, not immediately after casting it. If the spell is countered, you don't get the addendum bonus.
(wotc • 2024-01-12)
If an effect copies a spell with an addendum ability while it's on the stack, the copy wasn't cast at all, so you won't get the addendum bonus.
(wotc • 2024-01-12)
Rulings
Addendum abilities of instant spells apply while the spell is resolving, not immediately after casting it. If the spell is countered, you don't get the addendum bonus.
(wotc • 2024-01-12)
If an effect copies a spell with an addendum ability while it's on the stack, the copy wasn't cast at all, so you won't get the addendum bonus.
(wotc • 2024-01-12)