Bloodmoon Assassins using Shroud of Stealth will NOT appear on ranger tracking unless they cast Skylight Sagacity BEFORE hitting the track button. Casting Skylight will not change the mobs on track if the track window is already up and Skylight fading is not a concern as the assassins on your track list will not disapear from it until you close the track window.
These mobs have Shroud of Stealth - they can only be seen with a see invis v2 (wiz spell aspect of Zomm works). They also can cast Distraction (the Mez one) on a character allowing them to lose aggro with that character.
Their SoS ability has a reuse timer, so they can reactivate it quickly once, but if they use it again, it takes them a few minutes to be able to use it again.
They have the rogue aa ability Shroud of Stealth.. Pretty sure you can see em with https://everquest.allakhazam.com/db/spell.html?spell=15079 . But you'de have to ask a ranger if you can find one not crying about the HOA nerf. Anyway be glad they didnt give them Daggerfall