Need help to unlock a skin

Can someone please tell me how can I unlock the power of the alliance skin??

 

If you hover your mouse over the item when in the Customization window, it tells you that it is awarded once you've completed a specific achievement. If you look that up, it seems you need to kill 999 Guardians, Champions, Leaders, Sentinels or Bosses while using the Power of Alliance as your weapon.

Not sure if that is what you were asking....

 

I thought I got that particular skin the other day by dropping the weapon. I've been bouncing around doing a lot of quest & farming gear, so can't remember where exactly. You can hover over the item in the customization window at the blacksmith like Dragonnns said to see. Once you're in the customization window, you can also left-click your weapon in the right-hand window, so it'll only show those particular skin for that slot to save scrolling through everything.

 

The basic weapon/skin drops from khalys and nefertari (not the PW bosses i think, just the normal ones)

The effect of it unlocks as @Dragonnns allready said by killing 999 Guardians, Champions, Leaders, Sentinels or Bosses while using the Power of Alliance as your weapon.