What the achievement asks
Kill 30 bosses in Grand Hunts. Fifteen points, account-wide.
One hunt has one boss, so this is thirty hunts. It is the longest of the three Grand Hunt achievements and the one to plan around.
What counts as the boss
The boss is the final creature of the hunt, the one killed immediately before Scout Tomul calls the end of the hunt and asks for the horn to be sounded. Nothing earlier in the chain counts.
That has a useful consequence: you can miss an entire hunt and still get credit. Arrive at the last stage, tag the final creature, and the kill counts exactly as much as if you had followed the party from the start.
So when a hunt shows on your map and you have ten minutes, go anyway. The last stage is where the achievement lives.
Presence is not enough here, unlike the steps of Longhunter. You have to actually tag the boss: land a hit, a heal on someone fighting it, anything that puts you on its list. Players report tagged bosses occasionally failing to register even so, so if you are running for the count, hit it early rather than arriving as it dies.
If your counter goes backwards
This achievement had a genuine and well-documented bug at launch where the counter reset: players watched it fall from eighteen to one, and a server restart zeroed it for others. It was hotfixed in December 2022 and has behaved since.
A separate oddity worth knowing: some players find kills not counting while solo, and counting again after spending a few minutes in a party. If your count is stuck, join any group before the next hunt and see whether it starts moving.
Where it fits
One of eleven under Flight Club, a piece of A World Awoken. Thirty hunts is far more than the hundred steps of Longhunter needs, so that one finishes on the way, and every hunt is also a chance at the colours in Tetrachromancer.