X-costed cards and damage

[theinfamoose327]

My friends and I were discussing this the other day, and I couldn't really find any concrete answers, so I thought I'd turn here. If I were to return, say Burn from within from my graveyard to my hand using Volcanic Vision, what would happen? I thought that VV would deal damage equal to what I paid on bfw (for example, I paid 4 four the X cost, so it would deal 5). My friend contested it would only deal 1. What is the correct answer? thanks for your help.

[WWolfe]

It would only deal 1 damage. Burn From Within's CMC is 1 as X is considered a variable casting cost and has no value towards CMC. This is true for all spells that contain X in their casting cost.

[DelverMage]

I second WWolfes answer. 

The value of X, when it comes to CMC is 0, when it is not on the stack.

This is a copy of the official rule in the comprehensive rules document, Guilds of Ravnica edition.

202.3e When calculating the converted mana cost of an object with an {X} in its mana cost, X is treated as 0 while the object is not on the stack, and X is treated as the number chosen for it while the object is on the stack.