Haunted Memento nerfed for server stability
Back in patch 6.0, the plague event drop Haunted Memento was nerfed to provide a random, 15-second haunting, rather than provide a constant ghastly companion. Many who owned the item didn't notice the change ... but those who did notice weren't too happy. The item, no longer able to be acquired, was something special. Why the change? Community managed Bashiok shed some light on the subject:
The Haunted Memento being the #1 source of creature spawns is somewhat fascinating -- given the (perceived?) rarity of the item, we were surprised by that spawnrate. Even with the creature respawning every time a player zoned or took a flight point, we wouldn't have expected it to be so significant. The nerf to the item is unfortunate -- especially given reports that the ghost's spawn buff can break players out of stealth -- but it seems necessary given this information. However, if the item does break stealth, hopefully that's a bug that can be fixed.