Perhaps some examples would help:
let's say I have a
Sun Titan
on the field and you have a
Loxodon Smiter
and there are no other nonland permanents on the field.
You have a
Oblivion Ring
in your hand that you're itching to use on my Titan.
You cast the Ring, you are not required to announce a target at this point because Oblivion Ring the spell has no target (it's not an aura like
Arrest
). You can announce a target when you cast it, but I'll come back to that later.
A spell can be responded to. I can
Negate
it for example and Ring will never hit the field. So its trigger would never trigger.
I could cast
Unsummon
targeting my Titan in response to the spell as well and my Unsummon would bounce the Titan back to my hand and then Ring would resolve and enter the field.
Once Ring hits the field, its ability triggers (going to the stack, while Ring stays on the field) and you are required now to choose a legal target for it, assuming there is one (if there isn't one, the trigger is just removed from the stack)
If I had no response to your Ring spell, then it'll enter the field and trigger and you'll choose to target my Titan.
Now Ring's trigger is on the stack and can also be responded to.
eg. I could
Voidslime
it to save my Titan or I could cast Unsummon at my Titan and make the trigger's only target illegal (countering the trigger when it goes to resolve).
Now let's say I cast the Unsummon at my Titan, depending on when I cast it the result will be different.
I can cast it in response to the Ring spell or the Ring trigger.
If I cast it at my Titan in response to the Ring spell, you will have to choose a legal target for the Ring trigger when Ring enters the field (yes, you'd have to exile your own Smiter in this example as you can't choose the Ring itself because it says
another nonland permanent, but
if I did have another nonland permanent you could choose to exile it though)
If I cast Unsummon at my Titan after Ring resolves and enters the field in response to its trigger, then the trigger won't exile anything because it will be countered.
Ring gets even weirder, let's say I don't respond to the Ring spell or the Ring trigger and the Ring trigger is still on the stack and you have a
Boomerang
in hand.
You could cast Boomerang at your own Ring. Boomerang would resolve and return Ring to your hand and this would trigger Ring's leave the field trigger and place it on top of its first trigger (which is still waiting to resolve). Ring's leaves the field trigger will then resolve and return nothing (because nothing has been exiled yet) and then Ring's first trigger will resolve and exile my Titan permanently.
Now earlier I said that you can indicate the target of Ring when you cast it. This is true, but you need to understand that you are actually proposing a shortcut of future events to your opponent.
Saying "I ring your Titan" is really saying "I cast Ring as a spell. I assume you have no response so it resolves and enters the field where it triggers and I will choose your Titan to exile and I assume you have no response so its trigger resolves and your Titan is exiled."
It has a built in assumption that your opponent won't repond - he might
Cancel
it, he might
Unsummon
his Titan, you don't know.
If your opponent says "Ok" then he accepts the sequence of events as you proposed them.
If he chooses to respond, he should indicate at what point he's responding (unless it's obvious)
eg.
Counterspell
won't do anything to the triggered ability.
and if he does respond, you aren't bound by the shortcut you proposed from the point of response onwards.
eg. if he Unsummons his Titan in response to the Ring spell, you have to choose another legal target even if it means you have to target your own Smiter.
MtG Rules Advisor &
Goth/Industrial/EBM/Indie/Alternative/80's-Wave DJDJ VortexDCI Certified Rules Advisor from July 14, 2009 to July 14, 2012
DCI #5209514320
Wit found in Rules Q&ARPJesus: "Man, screw the rules, I'll play a game of 2HG Archenemy Planechase Emperor EDH draft yet. Once I figure out the rules for it..."
Chaikov: "Of course, casual Magic may be played any way your Pokemon group agrees on..." and "It's not logic. It's Magic!"
GainsBanding: "I only play online. The Magic Online shuffler is AWESOME!"
Ikegami: "one might think [adult cats] would make excellent tokens. The issue, though, is that they are very hard to exile. They return to the battlefield more often than an undying creature."
Astarael7: "Does 121.1 imply that players are supposed to wear their poison counters?"
Bimmerbot: "If you move the wrong way and [the poison counters] fall, it's a game rule violation"
Helluminatus: "Just remember, if it looks like a duck, smells like a duck, and quacks like a duck, but the oracle text says
creature - Bunny , then by god, it's a bunny."
MadCow21: "Who are you and what have you done with the real Chaikov?"
My Wife's Makeup Artist Page <-- cool stuff - check it out