Hmmm, perhaps a Free Company thing?

*Talk to Free Company NM Tracker*

"Oh, why if it isn't <player name>. Word around here is you and your <free company name> have been hunting down some pretty notorious beasts. I got me here an official hunt order from the <important faction> to track down somethin' by the name of <HNM name>. You and your <free company name> up for the challenge?"

Yes<

"Knew you wouldn't turn down such an opportunity! Here's a special Levecard. I've marked the area on the map of where you can find your target. Remember that only members of your Free Company whom possess this Levecard can track the target."

-You receive the 'Purple Rage' Levecard.-

*Travel to an area indicated on your map in a high level area. Approach (!?) on your map with all Free Company members in range.*

"There are freshly made tracks here in the sand/grass/snow/blah blah....Are you ready?"

Yes<

-Behemoth Spawns, Fight Behemoth, Defeat Behemoth-

"Each party member receives a {Trophy Behemoth Hide} key item."

Return to Free Company Tracker quest giver to turn in the Key Item for a reward. (Behemoth weapon, Behemoth armor, Behemoth Accessory, Gil)