Fast Talker  

House of Thule -> Conquest -> Fast Talker
"This special challenge can be completed during the mission "Hippity Hoppity Kill"
[ ] Speak to Tergan, Nalder, Thaelin, and Saena in less than 10 seconds.

Strat: This achievement is done during the middle part of the mission, when the following task steps open up:

Find Tergan Norwath 0/1 (Morell's Castle)
???
Find Nalder Rallin 0/1 (Morell's Castle)
???
Find Thaelin Mhorna 0/1 (Morell's Castle)
???
Find Saena Kinde 0/1 (Morell's Castle)
???

You will need 4 different group members to move to the 4 NPCs and coordinate so that all 4 NPCs are hailed at the same time (within 10 seconds). Stay invisible to keep from getting agro from the imps that spawn. It is possible but somewhat difficult to do this with 3 group members, with one person moving between Tergan and Nalder who are both in the forest, but you would have to be very fast and adept, using cheetah or bard speed. It is not possible to get the achievement with only 1 or 2 people.

If you succeed the Fast Talker achievement, it is granted at the moment you complete the 4 hails, or at least within a few seconds of that, for all players in the instance (unless your character achieved it already).