<p>Yes, your interpretation is correct. From the card rulings:</p>
<blockquote>
<p>Conduit of Ruin’s last ability doesn’t change the mana cost or
converted mana cost of any spell. It changes only the total cost you
actually pay.</p>
<p>If you control more than one
Conduit of Ruin, the last ability of each of them applies only to the
first creature spell you cast each turn, not to different spells; if you control two Conduits of Ruin, the
first creature spell you cast each turn will cost {4} less.</p>
<p>If the first creature spell you cast in a turn has {X} in
its mana cost, you choose the value of X before calculating the
spell’s total cost. For example, if the first creature spell you cast
in a turn has a mana cost of {X}{G}, you could choose 2 as the value
of X and pay {G} to cast the spell.</p>
</blockquote>
<p>So, the value that you pick for X is fixed, the only thing that changes is what you actually pay.</p>

CC BY-SA 3.0
2015-12-04T12:25:24.883Z
2015-12-04T12:25:24.883Z
2020-06-17T09:01:24.697Z
Nuclear Hoagie
<p>You choose a value for X which is then reduced by two colourless mana for each conduit you have on the battlefield.</p>

<blockquote>
  <p>If I have a Conduit of Ruin on the battlefield and say that I will be
  casting Endless One for 10 mana, will the cost reduction of 2 mana
  from the Conduit's effect reduce the X so that the Endless one is 8/8
  or will it remain 10/10?</p>
</blockquote>

<p>You choose a value for X and then a slew of effects may either increase or decrease the cost. Here is the pertinent rules. It is a bit long but worth the read.</p>

<blockquote>
  <p>601.2a To propose the casting of a spell, a player first moves that card (or that copy of a card) from where it is to the stack. It
  becomes the topmost object on the stack. It has all the
  characteristics of the card (or the copy of a card) associated with
  it, and that player becomes its controller. The spell remains on the
  stack until it’s countered, it resolves, or an effect moves it
  elsewhere.</p>
  
  <p>601.2b If the spell is modal, the player announces the mode choice (see rule 700.2). If the player wishes to splice any cards onto the
  spell (see rule 702.46), he or she reveals those cards in his or her
  hand. If the spell has alternative or additional costs that will be
  paid as it’s being cast such as buyback or kicker costs (see rules
  117.8 and 117.9), the player announces his or her intentions to pay any or all of those costs (see rule 601.2f). A player can’t apply two
  alternative methods of casting or two alternative costs to a single
  spell. <strong>If the spell has a variable cost that will be paid as it’s
  being cast (such as an {X} in its mana cost; see rule 107.3)</strong>, the
  player announces the value of that variable. If a cost that will be
  paid as the spell is being cast includes hybrid mana symbols, the
  player announces the nonhybrid equivalent cost he or she intends to
  pay. If a cost that will be paid as the spell is being cast includes
  Phyrexian mana symbols, the player announces whether he or she intends
  to pay 2 life or the corresponding colored mana cost for each of those
  symbols. Previously made choices (such as choosing to cast a spell
  with flashback from a graveyard or choosing to cast a creature with
  morph face down) may restrict the player’s options when making these
  choices.</p>
  
  <p>601.2f The player determines the total cost of the spell. Usually this is just the mana cost. Some spells have additional or alternative
  costs. Some effects may increase or reduce the cost to pay, or may
  provide other alternative costs. Costs may include paying mana,
  tapping permanents, sacrificing permanents, discarding cards, and so
  on. The total cost is the mana cost or alternative cost (as determined
  in rule 601.2b), plus all additional costs and cost increases, and
  minus all cost reductions. If multiple cost reductions apply, the
  player may apply them in any order. If the mana component of the total
  cost is reduced to nothing by cost reduction effects, it is considered
  to be {0}. It can’t be reduced to less than {0}. Once the total cost
  is determined, any effects that directly affect the total cost are
  applied. Then the resulting total cost becomes “locked in.” If effects
  would change the total cost after this time, they have no effect.</p>
</blockquote>

CC BY-SA 3.0
2015-12-04T18:37:19.283Z
I think it would improve this answer to specifically say that the value of X is not reduced by the cost reduction mechanisms. Also, you posted 3 large paragraphs of rules quotations and bolded half a sentence (and that half doesn't really say anything alone). I would suggest emphasizing all of the parts that you think are relevant and/or skipping the parts that are irrelevant.
murgatroid99
CC BY-SA 3.0
2015-12-04T14:11:21.730Z
2015-12-04T14:11:21.730Z
Neil Meyer
<p>If I have a <a class="mtg-autocard" target="_blank" rel="noreferrer" href="https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Conduit%20of%20Ruin">Conduit of Ruin</a> on the battlefield and say that I will be casting <a class="mtg-autocard" target="_blank" rel="noreferrer" href="https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Endless%20One">Endless One</a> for 10 mana, will the cost reduction of 2 mana from the <a class="mtg-autocard" target="_blank" rel="noreferrer" href="https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Conduit%20of%20Ruin">Conduit of Ruin</a>'s effect reduce the X so that the <a class="mtg-autocard" target="_blank" rel="noreferrer" href="https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Endless%20One">Endless One</a> is 8/8 or will it remain 10/10?</p>
<p>My thinking is going with X = 10, but I need to make sure.</p>
<p>Then, expanding on that:</p>
<p>If I have 4 x <a class="mtg-autocard" target="_blank" rel="noreferrer" href="https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Conduit%20of%20Ruin">Conduit of Ruin</a> on the battlefield, could I cast an 8/8 <a class="mtg-autocard" target="_blank" rel="noreferrer" href="https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Endless%20One">Endless One</a> for &quot;free&quot;, using only the total cost reduction of 8 mana (from the 4 x <a class="mtg-autocard" target="_blank" rel="noreferrer" href="https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Conduit%20of%20Ruin">Conduit of Ruin</a>s) as the &quot;X&quot; casting cost?</p>

CC BY-SA 3.0
2015-12-05T16:30:24.690Z
You might think of it like this (summarizing the answers, which is why I put it as a comment which can be temporary): Conduit changes the _cost_, it doesn't change the X.
David Z
CC BY-SA 3.0
2015-12-06T00:28:03.450Z
Your first and second example process the cards differently. If you reduced X from the amount of mana you want to pay for each Conduit like you did in the first example it would be a -8. The Conduit allows you to increase X without spending more mana, not decrease it from the amount spent. So for 10 mana you can get a 12/12 not an 8/8.
Fr33dan
<magic-the-gathering>
"Conduit of Ruin" and "Endless One"
user2959229
# "Conduit of Ruin" and "Endless One"

(Asked by: username_0 on 2015-12-04)

If I have a [Conduit of Ruin](https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Conduit%20of%20Ruin) on the battlefield and say that I will be casting [Endless One](https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Endless%20One) for 10 mana, will the cost reduction of 2 mana from the [Conduit of Ruin](https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Conduit%20of%20Ruin)'s effect reduce the X so that the [Endless One](https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Endless%20One) is 8/8 or will it remain 10/10?

My thinking is going with X = 10, but I need to make sure.

Then, expanding on that:

If I have 4 x [Conduit of Ruin](https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Conduit%20of%20Ruin) on the battlefield, could I cast an 8/8 [Endless One](https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Endless%20One) for "free", using only the total cost reduction of 8 mana (from the 4 x [Conduit of Ruin](https://gatherer.wizards.com/Pages/Card/Details.aspx?name=Conduit%20of%20Ruin)s) as the "X" casting cost?

**Tags:** magic-the-gathering

> **Comments:**
> **username_1**: You might think of it like this (summarizing the answers, which is why I put it as a comment which can be temporary): Conduit changes the _cost_, it doesn't change the X.  
> **username_2**: Your first and second example process the cards differently. If you reduced X from the amount of mana you want to pay for each Conduit like you did in the first example it would be a -8. The Conduit allows you to increase X without spending more mana, not decrease it from the amount spent. So for 10 mana you can get a 12/12 not an 8/8.  

---

## 2 answers

### Answer by username_3 on 2015-12-04. Score: 6 | Accepted answer

Yes, your interpretation is correct. From the card rulings:

> Conduit of Ruin’s last ability doesn’t change the mana cost or
> converted mana cost of any spell. It changes only the total cost you
> actually pay.
>
> If you control more than one
> Conduit of Ruin, the last ability of each of them applies only to the
> first creature spell you cast each turn, not to different spells; if you control two Conduits of Ruin, the
> first creature spell you cast each turn will cost {4} less.
>
> If the first creature spell you cast in a turn has {X} in
> its mana cost, you choose the value of X before calculating the
> spell’s total cost. For example, if the first creature spell you cast
> in a turn has a mana cost of {X}{G}, you could choose 2 as the value
> of X and pay {G} to cast the spell.

So, the value that you pick for X is fixed, the only thing that changes is what you actually pay.


---

### Answer by username_4 on 2015-12-04. Score: 0

You choose a value for X which is then reduced by two colourless mana for each conduit you have on the battlefield.

> If I have a Conduit of Ruin on the battlefield and say that I will be
> casting Endless One for 10 mana, will the cost reduction of 2 mana
> from the Conduit's effect reduce the X so that the Endless one is 8/8
> or will it remain 10/10?

You choose a value for X and then a slew of effects may either increase or decrease the cost. Here is the pertinent rules. It is a bit long but worth the read.

> 601.2a To propose the casting of a spell, a player first moves that card (or that copy of a card) from where it is to the stack. It
> becomes the topmost object on the stack. It has all the
> characteristics of the card (or the copy of a card) associated with
> it, and that player becomes its controller. The spell remains on the
> stack until it’s countered, it resolves, or an effect moves it
> elsewhere.
>
> 601.2b If the spell is modal, the player announces the mode choice (see rule 700.2). If the player wishes to splice any cards onto the
> spell (see rule 702.46), he or she reveals those cards in his or her
> hand. If the spell has alternative or additional costs that will be
> paid as it’s being cast such as buyback or kicker costs (see rules
> 117.8 and 117.9), the player announces his or her intentions to pay any or all of those costs (see rule 601.2f). A player can’t apply two
> alternative methods of casting or two alternative costs to a single
> spell. **If the spell has a variable cost that will be paid as it’s
> being cast (such as an {X} in its mana cost; see rule 107.3)**, the
> player announces the value of that variable. If a cost that will be
> paid as the spell is being cast includes hybrid mana symbols, the
> player announces the nonhybrid equivalent cost he or she intends to
> pay. If a cost that will be paid as the spell is being cast includes
> Phyrexian mana symbols, the player announces whether he or she intends
> to pay 2 life or the corresponding colored mana cost for each of those
> symbols. Previously made choices (such as choosing to cast a spell
> with flashback from a graveyard or choosing to cast a creature with
> morph face down) may restrict the player’s options when making these
> choices.
>
> 601.2f The player determines the total cost of the spell. Usually this is just the mana cost. Some spells have additional or alternative
> costs. Some effects may increase or reduce the cost to pay, or may
> provide other alternative costs. Costs may include paying mana,
> tapping permanents, sacrificing permanents, discarding cards, and so
> on. The total cost is the mana cost or alternative cost (as determined
> in rule 601.2b), plus all additional costs and cost increases, and
> minus all cost reductions. If multiple cost reductions apply, the
> player may apply them in any order. If the mana component of the total
> cost is reduced to nothing by cost reduction effects, it is considered
> to be {0}. It can’t be reduced to less than {0}. Once the total cost
> is determined, any effects that directly affect the total cost are
> applied. Then the resulting total cost becomes “locked in.” If effects
> would change the total cost after this time, they have no effect.

> **Comments:**
> **username_5**: I think it would improve this answer to specifically say that the value of X is not reduced by the cost reduction mechanisms. Also, you posted 3 large paragraphs of rules quotations and bolded half a sentence (and that half doesn't really say anything alone). I would suggest emphasizing all of the parts that you think are relevant and/or skipping the parts that are irrelevant.  

---

