Converted Mana Cost on the Stack

[Morganator 2.0]

This is something that has been bothering me for a while. How does converted mana cost on the stack work? I've been searching around the rules and found conflicting answers. The example for rule 601.3a says.

A player controls Void Winnower, which reads in part, “Your opponents can't cast spells with even converted mana costs.” That player’s opponent may begin to cast Rolling Thunder, a card whose mana cost is {X}{R}{R}, because the chosen value of X may cause the spell’s converted mana cost to become odd.

I always thought the converted mana cost of a spell couldn't change, but now I see that it can differ while on the stack. And while I found stuff for cards with {X} in their mana cost, I didn't find anything for cards with additional costs (like kicker) or alternate costs (Flashback, Overload). So I'm going to give some examples, and hopefully someone can explain what happens.

• Fireball is cast, where X equals 4 and they paid 2 mana for two targets. If Mana Drain is used to counter it, how much mana will the controller of Mana Drain get?
• Can a player overload Cyclonic Rift if Gaddock Teeg is on the battlefield?
• A player controls Lavinia, Azorius Renegade. If their opponent only has two lands, can they pay the kicker cost for Blink of an Eye (using mana from artifacts)?
• Can a player flashback Ancient Grudge if their opponent controls Void Winnower?

[Soren841]

Cmc for fireball X=4 would be 5. X affects cmc on the stack.

[WWolfe]

Flashback doesn't change the converted mana cost of the spell itself. It's just paying an alternate cost. The same is true for Overload and Kicker.

https://mtg.gamepedia.com/Flashback#Rulings

https://mtg.gamepedia.com/Overload#Rulings

https://mtg.gamepedia.com/Kicker#Rulings

ETA- Mana Drain would take what the converted mana cost is while the spell is on the stack, I've actually been involved in a game where this situation was questioned and a judge was called over.

[WWolfe]

One other situation- Morph cards. It too is an alternate cost, it's CMC is considered to be 0.

702.34b To cast a card using its morph ability, turn it face down. It becomes a 2/2 face-down
creature card, with no text, no name, no subtypes, no expansion symbol, and no mana cost. Any
effects or prohibitions that would apply to casting a card with these characteristics (and not the
face-up card’s characteristics) are applied to casting this card.

ETA ruling

[Morganator 2.0]

What about cards like Thalia, Guardian of Thraben? Does this change CMC on the stack?

[WWolfe]

Cost reduction doesn't effect the spells CMC. It's still considered as having the printed CMC.

[ApothecaryGeist]

The converted mana cost of a spell is whatever is printed on the upper right-hand corner, with all mana symbols converted into a single number.  Whenever there is an X in the cost, it is considered to be 0 everywhere except the stack.  While on the stack, X has whatever value was declared for it.

Any card with multiple faces (transform cards, splilt cards, melded cards) have the total converted mana cost of all sides of it everywhere except the stack.  When casting a split card, only the half that is cast is considered when determining its converted mana cost.  The other half is ignored.

Face-down cards with morph/manifest are considered to have a converted mana cost of 0.  This is by rule, as they had to be assigned something that is public knowledge.

The amount of mana you pay for a spell may or may not be equal to its converted mana cost.  Paying an alternate cost like flashback or overload does not change the CMC.  (An overloaded Cyclonic Rift still has a CMC of 2.)

To determine the amount of mana you pay, start with the mana cost printed on the card.  (X needs to be declared when the spell is put on the stack.)  Then apply any alternate costs (like flashback).  Then apply any cost increases (like Kiora's Dismissal), then apply any cost reductions (like Pearl Medallion).  Then that is how much mana you pay.  Technically this calculation happens every time you put a spell/effect on the stack.

Happy Brewing!

[Morganator 2.0]

So let me see if I understand this. If someone casts Green Sun's Zenith where X=1, Mental Misstep can't counter it but Spell Snare can?

[Mostlynotgay]

So let me see if I understand this. If someone casts Green Sun's Zenith where X=1, Mental Misstep can't counter it but Spell Snare can?

d(^^d) bingo

When a spell has X in the cost, x = 0 for the purpose of calculating CMC.
The *ONLY* time X is not zero is when it is on the stack (though x could be zero there, too, if you case with x being zero, like casting Hangarback Walker for 0 to get a death trigger or something)

And the alternate value for X only exists on the stack. So if I cast Hangarback Walker X=10 and it resolves, my opponent can destroy it with a ratchet bomb with no counters because even though I CAST it with x=10 (so a 20cmc on the stack), on the.battlefield x=0