Set Up a private unleashed wolfpack session
You can do this by your self if you can't be bothered to find a partner like me!
I did it on Saint-pierre
Choose blackbeard and make sure you have the pistol unlocked at level 38 or purchased with EC using real money and equip it to your ability set
Once you get to the defend chest wave, stand on cart above the one chest and look at the other
Once both chests are being attacked lock on far attacker
and shoot him
don't forget to hold
so you don't miss the shot,
Then quickly hang on ledge of cart with
Lock on to Second attacker under you if hes invisible, if hes not then you don't have to lock on him, and hit
for acrobatic kill.
And achievement Unlocked Hope this Helps