Cards with "x" and chalice

[WhiteMage05]

The ruling on cards with X in the casting cost is that while on the stack, X becomes the declared amount. But in cases such as Decree of Justice and Skeletal Scrying, I don't want to declare X until the spell resolves and then pump mana into it.

How does chalice effect this? If chalice is at 1, can I scry with the intent to pump mana into it? If chalice is at 3, can I cycle DoJ with the same intent?

Thanks in advance.

-WhiteMage05

[ProZachar]

The ruling on cards with X in the casting cost is that while on the stack, X becomes the declared amount. But in cases such as Decree of Justice and Skeletal Scrying, I don't want to declare X until the spell resolves and then pump mana into it.

How does chalice effect this? If chalice is at 1, can I scry with the intent to pump mana into it? If chalice is at 3, can I cycle DoJ with the same intent?

Thanks in advance.

-WhiteMage05

First, cycling Decree of Justice and playing Skeletal Scrying are different beasts.  Chalice has no effect on the soldier making part of DoJ, as Chalice only triggers on a player playing a spell.  Cycling DoJ isn't playing a spell.

Now, when you play a spell with X in its mana cost, you must declare (and pay) X up front.  You cannot pay B for Scrying, wait to see if it gets countered, and then try to pump more mana into it to draw cards.  Everybody will know the value of X, and you will have paid BX, by the time you are done playing the spell.

Cycling Decree of Justice to make soliders follows diffferent rules.  The solider making part of DoJ triggers off you cycling it.  Triggered abilities are usually written "When/Whenever/At <time>, <effect>".  When <time> occurs, the ability goes on the stack.  The instructions that go on the stack are <effect>.  So, with Decree of Justice:

When you cycle Decree of Justice, you may pay X. If you do, put X 1/1 white Soldier creature tokens into play.

<time> is "you cycle Decree of Justice" and <effect> is "you may pay X. If you do, put X 1/1 white Soldier creature tokens into play."  That mana payment takes place when the triggered ability resolves.  This is why you can (actually, you have to) wait to see if the ability will get Stifled before you put any mana into it.

[epeeguy]

The ruling on cards with X in the casting cost is that while on the stack, X becomes the declared amount. But in cases such as Decree of Justice and Skeletal Scrying, I don't want to declare X until the spell resolves and then pump mana into it.

You cannot play a spell in this manner.  When you play the spell, you must declare what value X has, as in order to play the spell, you must pay all costs associated with it.  Therefore, when you play Skeletal Scrying, you must declare the value that X and then pay the costs (which is both the mana cost and discarding of card).  You cannot wait until the spell resolves to determine how much X is.

The appropriate rules governing this are 409.1b and 409.1f (part of 409 "Playing Spells and Activated Abilities").

So, when you play Skeletal Scrying, the Chalice will see the converted mana cost of the spell (which is whatever value X was set to plus the for the part of the cost) and trigger if this is equal to the number of charge counters on the Chalice.  You cannot wait until later to determine the cost and avoid the Chalice's effect.