Hearthpwn

Card is stronger when ahead in mana, but that only occurs when already winning.

Does this card have any use on turn10+?

Not in warlock, no.

The golden Art of this card looks amazing

The problem is at 6 mana the impact of ramp is severely diminished, so this is riding purely on the mana deramp of the opponent, and at those stats it might not be good enough.

i don't think so.. In the case that you had the coin this is decent , but if you start then at 6st turn with no other ramp this will push you to 7 and your enemy from 5 back to 4 basicly another 5 mana turn,to battle your next 8mana turn..

Ramping is one thing,but stealing other player's mana distrupting there play and curve is on a whole another level