Lets say I am casting Oblivion Sower. The on-cast effect would activate, exiling the top 4 cards of my opponents deck. The person decides to cast Mana Leak to counter my creature. Assuming I don't have enough mana to prevent the Mana Leak on my own, could I tap the lands, assuming I get three, that are exiled with Oblivion Sower to prevent Mana Leak from countering my creature?

Oblivion SowerMana Leak

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    Today I learned that "in response to" is an actual phrase in the comprehensive rules glossary (I always thought it was player slang). It means to cast something while another object is on the stack. In this case you have two objects on the stack, and so the question needs clarification. When exactly did your opponent cast Mana Leak? Before, or after Oblivion Sower's trigger resolved? – Rainbolt Oct 4 '17 at 14:52
  • @Rainbolt it was a more casual game, so I don't think we truly specified. Also probably because we didn't really separate the on cast trigger and the spell itself. We are still learning. – Shadow Z. Oct 4 '17 at 15:39

You would not be able to use the lands gained by Oblivion Sower to pay Mana Leak's cost.

The reason for this is that you will not have those lands when you need to Pay Mana Leak's cost.

Here is the interaction broken down step by step, assuming proper play from your opponent:

  1. You cast Oblivion Sower, it's ability goes onto the stack on top of it.
  2. Your Opponent responds to your spell by casting Mana Leak targeting your Oblivion Sower, Mana leak goes onto the stack on top of Oblivion Sowers Ability.
  3. Assuming no responses, the stack will now begin to resolve the spells/abilities.
  4. Mana Leak resolves, you must now pay the 3 generic mana or have your oblivion sower countered.
  5. The on-cast ability of Oblivion Sower resolves, you would now get your lands.
  6. If you paid the costs for Mana Leak, your Oblivion Sower would now resolve and enter the battlefield.

As you can see, at the time you need to pay Mana Leak's costs Oblivion Sower's ability is still on the stack, so no fresh lands for you (yet). It is also not possible for you opponent to respond to the Oblivion Sower before the cast trigger is on the stack, as no player is given priority when Oblivion Sower is cast until after its on cast ability goes onto the stack.

601.2i: Once the steps described in 601.2a–h are completed, effects that modify the characteristics of the spell as it’s cast are applied, then the spell becomes cast. Any abilities that trigger when a spell is cast or put onto the stack trigger at this time. If the spell’s controller had priority before casting it, he or she gets priority.

However your opponent can wait until after the Oblivion Sower's on cast ability resolves and then cast Mana Leak. In that situation you will have the lands, but this would have to be a deliberate choice by your opponent so it is unlikely for that to happen.

An Interesting note to keep in mind is that you will get the lands regardless of whether or not Oblivion Sower is succesfully countered, since the ability is triggered on cast.

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  • I'm sorry but I don't understand why the on-cast ability doesn't go on the stack in step 3. – sinsedrix Oct 5 '17 at 8:25
  • @sinsedrix "603.2. Whenever a game event or game state matches a triggered ability’s trigger event, that ability automatically triggers. The ability doesn’t do anything at this point." and "603.3. Once an ability has triggered, its controller puts it on the stack as an object that’s not a card the next time a player would receive priority." The trigger happens as you cast the Oblivion Sower, because that's what it says on the card. Then the next time any player gets priority, which is the moment you've finished casting the Oblivion Sower, the triggered ability goes on the stack. – Arthur Oct 5 '17 at 8:42
  • @sinsedrix No need to be sorry, everyone is here to help answer questions and understand MTG. Did @ Arthur's explanation help, or is there something else you need clarified? If you think the question is big/complicated enough feel free to ask it as a new question. – Malco Oct 5 '17 at 13:29
  • Thanks @Malco,it's maybe a bit tricky for me. The statement "that ability automatically triggers.The ability doesn’t do anything at this point" seems contractictory and set me confused. Also, I'm not at ease with the "priority" concept. – sinsedrix Oct 5 '17 at 13:55
  • There is a really good answer that might help you understand things over here: In plain English, how does casting spells and using creature abilities work with the stack and priority? Timing and priority is the back bone of MTG as it lets us know when you are allowed or not allowed to preform an action, it can be tough to understand the fiddly-bits of it. Most of the time you just need a basic understanding though. – Malco Oct 5 '17 at 14:07

It depends on exactly when your opponent casts Mana Leak; he can prevent you from doing so.

Your opponent has 2 options here... cast Mana Leak in response to the "when you cast" triggered ability, or to wait until that ability resolves, and then cast Mana Leak in response to the Oblivion Sower instead.

When you cast Oblivion Sower, the "when you cast" ability will go on the stack on top of the Oblivion Sower. At this point your opponent could cast Mana Leak on top of both of them, and the triggered ability will not have resolved yet, so you will not have those lands.

Note that even if Oblivion Sower is countered, the triggered ability will still resolve normally and you will still get the lands.

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  • Okay, so Oblivion Sower gets countered first, and I must pay the mana right then and there. And once the counter spell has finished on the stack, then the on cast effect would happen? So technically they could counter a spell after the on cast effect but still counter the spell, or they could counter it before the on cast effect, though it would still resolve. – Shadow Z. Oct 4 '17 at 15:35
  • @ShadowZ. does the explanation in my answer below help? I tried to be thorough and break it down step by step. – Malco Oct 4 '17 at 16:00
  • @ShadowZ. Okay, so Oblivion Sower gets countered first, and I must pay the mana right then and there. No. If you allowed Oblivion Sower to be countered, then you already lost your chance to pay for Mana Leak. You either pay, or the spell is countered. The two options are mutually exclusive. [...] then the on cast effect would happen? As the answer states, the on cast trigger happens regardless. – Rainbolt Oct 4 '17 at 21:08

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