Malchazeen

Malchazeen is an epic dagger. It is widely praised as one of the best mainhand daggers for PvE discovered in World of Warcraft thus far. It has a reddish glow surrounding the blade, which leaves a trail behind it, similar but more pronounced than Perdition's Blade. Unlike many other weapons with particle effects, many enchanting graphics stack on this dagger including the Mongoose enchant.

Statistically is is comparable to the Arena mainhand dagger however, statistically, this item is geared more for PvE, while the Arena weapons are geared towards PvP.

Thought of mainly as a Rogue mainhand weapon, this item is also quite a nice addition to Fury Spec Warriors as an offhand weapon, it is however not a good offhand weapon for Enhancement Shamans because of its fast speed.

Source
This item drops from Prince Malchezaar in Karazhan. Items that drop off Prince Malchezaar are often thought of as a tier above other items of a similar type in Karazhan, and this dagger is no exception.