2019-01-25
If the target creature is an illegal target by the time Arrester's Admonition tries to resolve, the spell doesn't resolve. You don't draw a card if you cast it during your main phase.
2024-01-12
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.
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.