I kept this cycle down for a while to see if there was anything else of significance on it, but it doesn't appear so:
The Fabled Grimfeather x26
a borer beetle x2
a griffawn x7
a griffenne x3
a griffon x1
a grizzly bear x4
a highland lion x4
a lioness x4
a pincer beetle x14
a silvermist wolf x4
a willowisp x7
Respawn definitely seems to be around 6 seconds as mentioned in another post. Spawn points are all over, but funnily enough, many of the more common locations seem aptly placed to wreak the most havoc (e.g. gypsy camp, guard tower, druid ring, cottage, etc.).
I popped into NK to get a pair for my alt and he was already up. Killed him and as soon as track updated he spawned again. I was only one in zone so I think he's on a Insta or 6 second respawn cycle. Killed the next two mobs that spawned right away (Highland lion, and a pincher beetle) and third mob was another fabled grimmy, lost the cycle after that (druid tracking isna't as good as ranja and I think the next spawn was on the other side of zone) but most spawns seemed to be on the west and or north of zone. hope that helps.
duo'd him tonight 66 bard and 66 shaman...was trying for the arms for baby zerker. the summoning was a pain, but easy enough to chant him down while shaman slowed/healed. found him closer to druid ring, pulled him to near gypsies. max hit was 580ish with 1357ac on bard
sheetz appassionato 66 Maestro of Shadows Bristlebane
So my guild on Rasp takes this guy out... I die during the fight(Midlevel rogue) get a port back and what do I see? Another Fabled Grimfeather fighting one of the ring druids... At 2% I attack and "You have slain The Fabled Grimfeather" You gain experience
Just soloed him tonight, wouldnt say it was easy, but it wasnt hard. took awhile to get him to spawn. i thought at first it was just griffs as PHers, but i got bored trying to find just griffs and killed everything in sight. that seemed to help out cause i found him just chillin, though maybe it was just griffs. slowed MOSTLY not fully as a post had mentioned. was easy just healing pet until slow wore off that almost got my pet lol.
I was fiddling with Fabled GrimFeather last night. He considered Dark Blue. I am a 65 Ranger and he hit me for a max of 528 (1220ac, combat stability 1, and combat agility 1 during the fight). Has a decent amount of HPs, but easily duo-able. I was able to proc Earthcaller on him so he is fully slowable. As all Fabled he is immune to run speed changes, and he DOES summon. Also, he is as fast as SoE. He does Enrage at 10%(as previously stated) so be careful.
I almost got him with a 52 cleric. I got wildly lucky and proc'd my Earthcaller on the very first hit. Cleric had C3 and we did fine until Grim Enraged(which I didn't know about at the time) and I ended up dieing cause I ate a nice quad of 528dmg hits.
As a bard, it was a simple matter of running a circuit around the zone to track any of the griffs. Don't limit yourself to running a small circle around the gypsy camp and guard tower...range out a bit farther than that (bard tracking only 100, go fig). Kill anything that flies. In the upper NW corner of the zone is one of those yellow column shrines...two griffs spawn from here. I don't think these two are PH's for ol'Grim, but I took'em out anyways. Grim was blue to my 63 bard, unmezzable and couldn't snare him. But, I easily outran him with Selos and pulled to our tank. He hit me for a max of 589. Rampages at 10%.
So, basically, kill all griffs in the zone..even The Silver Griffon...and Grim can spawn anywhere.