All of the mobs with Sentry in their name are immune to runspeed changes. This is definitely true for Halls of Honor, I'm not sure about Plane of Valor. They cannot be rooted or snared.
Cannot be snared/rooted.(none that I've faught) Can be mezzed. They may be able to be stunned(with an appropriate level stun) but am unsure. Slowable. Never tried to charm them, I prefer snarable mobs. They don't summon.
Their PHs are A Valorian Guardian(but not all guardians)
Never seen them drop parchments or the ring but have seen them drop most of the other loot listed above.
The spell Earthen Embrace does snare them. I've only had this bounce a few times. Regular snare does not work from what I've tried.
I did have the Wristband of Strategy drop today!! Woot, now that seems to be rare. First time I've seen it drop since I've been here. The Spectral Parchments do drop from time to time. The only consistent drops are Hero Parts, Brick of Ethereal Energy, and Strands of Ether.
just killed one at tents in Valor. Shaman slowed it. SK snared it, when snare faded it started walking off. Max hit was 583. 65 sk, 62 shm boxed, easy camp.