So, the Amulet does drop from Dreadtooth, on 10 Stacks, which I believe is the max. I don’t know if the amulet is a 100% drop, but I sure hope so XD Supposedly you may be able to get it from 9 too–but he must be Nightmareish for it to drop.
Going into the cave on 16-man HM and wearing the mask while using the amulet causes a boss called the “Dreadful Entity” to spawn.
I believe you get the title “Dread Slayer” upon defeating it.
But yes, a big congrats to Carnage Gaming! Sadly, the amulet has a 24 hour cooldown so you only get one attempt a day….though, currently, if traded (it can be traded for up to 2 hours like raid gear), it resets the timer so that’s probably going to be fixed eventually. You can also watch their stream here while they try 🙂
(and people thought I was crazy. HA.)
Edt: You do get the codex and title “Dread Slayer”. He also drops a Dreadful Orb.