Heartstone/Training Grounds and "X"

[Gorzo]

How do {Heartstone} and {Training Grounds} react with "X" cost activated abilities, such as on {Steel Hellkite}? Is the cost of X reduced, allowing you to make X a little larger should you so choose, or let you make X = 4 and pay 1 mana (if you had both grounds and stone in play)? Or is X not effected by these?

[ChrisRodriguez]

X is not affected by those cards. You still have to pay into X.

[BlackJester]

Gorzo is right. You announce the ability and put it on the stack. Then you announce variable values (in his example X=4). Choose targets. Determine costs (additional-reductions, so 4-2-1=1 ) and activate mana abilities. Then you pay the cost.

[BlackJester]

In this case X=1, 2, 3, or 4 would each cost a minimum of 1 mana.