Just some info on the quest line which leads to obtaining this amazing axe.
Shadow's Edge
Shadowmourne

The Sacred and the Corrupt
It is against my judgment that I present you this errand, <race>, as it will likely end in your undoing. Ignore my counsel and embark on the endeavor, and I shall provide you with the knowledge and resources to see it through.

You must return to Frostmourne Cavern and recover Light's Vengeance, Arthas' discarded hammer. Reforged with saronite and etched with the acidic blood of the Lich King's abominations, it will provide the foundation for our work.

Unholy Infusion
Before your weapon can reach its full potential it must be endowed with its signature powers. First among them is unholiness. You must seek out and defeat the one called Professor Putricide, but his death is not your only goal. You must use his resources against him.

Find a way to absorb his mutated slime. Use the foul substance to infuse your weapon with the power of the unholy. Only when this has been done shall I reveal your next task.

Blood Infusion
Your weapon is now prepared to be endowed with the power of blood. You are to face Queen Lana'thel in battle and bathe the axe in her Blood Mirror power. When it has been fully infused, you must slay her unmercifully.

May her screams pierce the ears of the Lich King as he awaits his fate.

Frost Infusion
Shadow's Edge is prepared to receive its final infusion of power. Sindragosa, the enemy's own mount, must fall. But before she is brought down, you must sustain three of her frozen breath attacks without tasting death.

Without his dragon, nothing shall stand between you and the Lich King.

The Splintered Throne
The Lich King's throne once served as his prison. Kil'jaeden himself crafted the vessel of icy crystals from the twisting nether. Its sole purpose was to hold Ner'zhul's vengeful spirit. When Arthas struck the crystal with Frostmourne, he released Ner'zhul's soul, allowing it to merge with with his own. Splinters from that impact are now scattered throughout the citadel.

I shall require those shards, held only by the Lich King's most powerful servants, to seal the power contained in your blade.

A Feast of Souls
Shadow's Edge is among the greatest weapons a <class> could hope to obtain. Is your lust for power sated, <race>? <You feel Mograine's penetrating gaze.>

I thought not. A final warning then... You now embark on the most treacherous leg of your quest. Bridle your aspirations, for if your aims are impure then your life, your very soul, is forfeit.

The weapon you hold is but an empty husk, a mere shadow of what it may become. Only the devouring of a thousand souls will unlock its true potential.
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To kinda sum it up it seems

1. Kill Rotface/Festergut and get 25 Primordial Saronite (think 25 crusader orbs when toc came out)

2 and 3. Kill Professor Putricide and Lana'thel

4. Kill Sindragosa after getting hit with 3 frost attacks while wielding Shadow's Edge.

5. Obtain 60 Shadowfrost Fragments which are held from the Lich King's most elite servants (bosses obviously) (think Valynar Fragments).

6. Slay 1000 trash mobs or bosses combination in Icecrown Citadel.
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