If the activated ability resolves but the targeted artifact isn't destroyed (perhaps because it has indestructible or it regenerates), Hoard-Smelter Dragon will still get the bonus.
01-01-2011
wotc
If the mana cost of a permanent includes {X}, that X is considered to be 0.
01-01-2011
wotc
If the targeted artifact is an illegal target by the time the activated ability resolves, the ability doesn't resolve. Hoard-Smelter Dragon won't get the bonus.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.