Quick and Durable is a dangerous combination. Even with it replacing itself with Goblin if used twice in a row (if I'm reading it correctly), other Quick cards could be used in between to pile up the damage for a relatively low cost. You might want to add a "No effect if New" on there to ensure that it's only used once per turn. Keep the clause about being played after itself as well, though, because as a Common Durable, you can expect it to appear in a hand more than once.
Even after all that, I still think it needs to cost more. The only other Swift/Quick Durables are Rare and cost 30 to 44 resources to deploy. Being Common, offering 9 attack, and having both Durable and Quick should have a heftier price tag.