How does Valakut work?

Question

Valakut, the Molten Pinnacle has an ability that says:

Whenever a Mountain enters the battlefield under your control, if you control at least five other Mountains, you may have Valakut, the Molten Pinnacle deal 3 damage to target creature or player.

Going by the wording, it appears that Valakut triggers every time a mountain enters the battlefield, and then checks the number of other mountains at resolution.

But then it has to deal 3 damage to a target.

My questions are:

• Does Valakut put another ability on the stack when this happens? If so, what kind of ability is it? Is it a triggered ability that can be copied with Strionic Resonator?
• If it's all the same ability, then does the controller of Valakut technically have to choose a target regardless of whether he has 5 other Mountains or not? So does a Valakut and one Mountain kill a Phantasmal Image?

Answer 1

You've partially answered your own question here: there is a single ability, which checks something on resolution. But it in fact checks the condition before triggering and on resolution! The fancy thing going on here is often called an "intervening if clause". Here's the detailed sequence of events:

• Valakut sees a Mountain enter the battlefield, and says "maybe I need to trigger!" The game checks to see if you have at least five other mountains, and if you do, the ability triggers and is placed on the stack. You choose the target here.
• Maybe other things happen in response?
• The ability resolves.
  • The ability checks again to see if you control at least five other mountains. (Maybe one got destroyed in the meantime?)
  • Assuming you do, it deals three damage to the chosen target.

Here's the relevant comp rule:

603.4. A triggered ability may read "When/Whenever/At [trigger event], if [condition], [effect]." When the trigger event occurs, the ability checks whether the stated condition is true. The ability triggers only if it is; otherwise it does nothing. If the ability triggers, it checks the stated condition again as it resolves. If the condition isn't true at that time, the ability is removed from the stack and does nothing. Note that this mirrors the check for legal targets. This rule is referred to as the "intervening 'if' clause" rule. (The word "if" has only its normal English meaning anywhere else in the text of a card; this rule only applies to an "if" that immediately follows a trigger condition.)

A side note: Evolve is a prominent recent example of a triggered ability with an intervening if clause. It doesn't target, but in some cases it can be very relevant that the ability checks again on resolution.

So for your specific questions:

No, there's no second ability, just the triggered ability which happens to check for a condition twice. But the ability is a triggered ability, and you can copy the whole thing with Strionic Resonator. The original and the copy will still check the "if" clause when they resolve.

If you don't have enough Mountains, you don't put the ability on the stack, so you don't choose a target, so no, you can't kill a Phantasmal Image with it.

Answer 2

603.4. A triggered ability may read "When/Whenever/At [trigger event], if [condition], [effect]." When the trigger event occurs, the ability checks whether the stated condition is true. The ability triggers only if it is; otherwise it does nothing. If the ability triggers, it checks the stated condition again as it resolves. If the condition isn't true at that time, the ability is removed from the stack and does nothing. Note that this mirrors the check for legal targets. This rule is referred to as the "intervening 'if' clause" rule. (The word "if" has only its normal English meaning anywhere else in the text of a card; this rule only applies to an "if" that immediately follows a trigger condition.) Example: Felidar Sovereign reads, "At the beginning of your upkeep, if you have 40 or more life, you win the game." Its controller's life total is checked as that player's upkeep begins. If that player has 39 or less life, the ability doesn't trigger at all. If that player has 40 or more life, the ability triggers and goes on the stack. As the ability resolves, that player's life total is checked again. If that player has 39 or less life at this time, the ability is removed from the stack and has no effect. If that player has 40 or more life at this time, the ability resolves and that player wins the game.

So to answer your questions:

Does Valakut put another ability on the stack when this happens?

No, only one ability is put on the stack if the "intervening 'if' clause" condition is met.

If so what kind of ability is it? is it a triggered ability that can be copied with Strionic Resonator?

Yes, it is a triggered ability that can be copied.

If it's all the same ability, then does the controller of valakut technically have to choose a target regardless of whether he has 5 other Mountains or not?

Targets are only chosen if the ability actually triggers. (IE. the player has 5 mountains in play.) So, no, one mountain is not enough to kill a phantasmal image.

Note the second part of CR603.4 I highlighted in bold: if when the ability resolves the player no longer has 5 mountains in play, the triggered ability will be removed from the stack and will do nothing. If the ability was duplicated with Strionic Resonator, of course that duplicated ability would also be removed.

Therefore, in the case where 5 mountains were in play and the ability triggers, a targeted phantasmal image would die even if in response their opponent destroyed enough mountains to drop the count and counter the ability. The triggered "this creature dies when targeted" ability would be on the stack at that point and could no longer be stopped if the spell is countered.