When can I cast an instant?
Asked by fastbond_stripmine_crucible 9 years ago
I was under the oppion that I can cast them at any given moment in the game not just in response to something which the person I was playing said because I tryed to kill his planes walker right after it entered the battle field with Hero's Downfall and he said I could not do it because I can't respond to a planeswalker entering the battle Field with an instant was he right
GoblinsInc says... #2
Some of the relevant rules.
116.1. Unless a spell or ability is instructing a player to take an action, which player can take actions at any given time is determined by a system of priority. The player with priority may cast spells, activate abilities, and take special actions.
116.1a. A player may cast an instant spell any time he or she has priority. A player may cast a noninstant spell during his or her main phase any time he or she has priority and the stack is empty.
116.3b. The active player receives priority after a spell or ability (other than a mana ability) resolves.
116.3d. If a player has priority and chooses not to take any actions, that player passes. If any mana is in that player's mana pool, he or she announces what mana is there. Then the next player in turn order receives priority.
April 18, 2016 8:48 p.m.
In addition to the other answers - yes, he is correct that you can't respond to a planeswalker (or anything else) entering the battlefield. The only thing you can respond to is an ability being put on the stack. So for example, if an Eternal Witness is cast, you can respond while it's on the stack. When it enters the battlefield, noone can cast spells or activate abilites before it's ETB ability is put on the stack - and that ability you can respond to once more. However, with only a Hero's Downfall, there's no way you can prevent the Witnesses ETB ability from triggering.
This is the reason why you can't kill Liliana of the Veil with a Lightning Bolt (unless the player controlling it lets you) - since the planeswalker doesn't have any ETB abilites, it's controller can activate one of their loyalty abilities (and therefore raising their loyalty) before you can take an action yourself. I think this is the example that GoblinsInc also was thinking of in his answer.
And in addition to the other rules, you won't also be able to cast an instant while a spell with Split-Second is on the stack.
GoblinsInc says... Accepted answer #1
You can cast an instant any time you have priority. While this seems like any time, it is slightly more limited.
If it is your opponent's turn, he is the active player. After any spell or ability resolves (in this case his planeswalker resolving and coming onto the field), the active player gains priority first. So before you can cast the spell (lets say lightning bolt), you have to wait for him to pass priority by deciding to not do more.
He can activate his planeswalker's ability first, then pass priority to you. When he has passed priority to you, you can cast the spell, but his planeswalker's ability is on the stack (with costs paid) and killing the walker won't remove the ability.
April 18, 2016 8:47 p.m.