What the achievement asks
Make use of ten things Fangcrack pulls out of the Portal to Torghast. Five points, account-wide.
Fifteen minutes of standing in one place, gated behind the Venthyr assault offering the quest "Fangcrack's Fan Club".
What counts
Fangcrack drags enemies out of the portal, and every so often something else comes with them.
Anima Power orbs. He throws them on the ground. Pick one up and it counts.
Ashen Phylacteries, the jars. Destroying one counts, but you need the killing blow, and there is a short window at the start where they take no damage. In a crowd, other people will take some off you.
The broker. Occasionally he pulls out a Torghast merchant, who sells Collapsing Riftstone at 100 Stygia, up to ten of them. Buying counts.
The trick for the anima powers
After three or four orbs, every further one you pick up turns into a broken placeholder power that awards nothing. This is not a limit on the achievement, it is a bug in how the powers stack on you.
Clear every anima power buff off yourself, then do a full logout and back in. Not alt-F4 and not a UI reload: type /camp. Logging out strips the powers, and the orbs become interactive again.
Where to stand
The edge of the platform. Fangcrack keeps pulling enemies out and they will kill themselves on him without your help, so there is no reason to be in the middle of it.
Progress on the phylacteries is not shared with your party, so if you are there with someone, split up rather than fighting over the same jar.
While you are there
The enemies Fangcrack drags out count toward the assault's own kill quest, so this is fifteen minutes that also finishes something else on your list.