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.
12-01-2024
wotc
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.
25-01-2019
wotc
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.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.
Lucas Graciano2019-01-25
