Star of Kellos is a gold treasure with the power "Monsters within 6 spaces of you lose the Undying ability". It would seem this is somewhat overpowered in RtL, due to the small dungeon sizes. In particular, my players are currently in the Valley of Souls, where all monsters have undying, but the Star of Kellos' large range covers an entire section of the dungeon. Given that some other range-based powers are nerfed (such as Spiritwalker and Rune Witch Astarra's glyph activation), it would make sense that this should be have reduced range as well, maybe reducing it from "within 6 spaces" to "within 3 spaces". I couldn't find any rulings on the forums or FAQ. Thoughts?

You can house rule it that way if you like. FFG hasn't said anything official about this item, so "officially" it still works out to 6 spaces. Considering how frequently I manage to make my undying saves anyway, I doubt I'd personally notice the difference =P

Considering the fact that in Gold heroes are too powerful and clean dungeons in 2 or 3 turns then i would say it is not. But yes the legendary of the gold level is a big dissapointment either you have or not the star of kellos and yes 99% of the times you will have it as legendary dungeons are mostly played on late level time so you will probably have it. In our campaigns our OL has a 60 to 70 of success in undying so it is pretty important for us to the point that we keep the cursed staff from the copper to cancel undying.