The Focusing Iris
The Focusing Iris is an orb found in the center of The Eye of Eternity and is used to summon Malygos.
Thrall: Twilight of the Aspects
Malygos had used his own blood to activate and control this orb, which had lain dormant for millennia. With the open Focusing Iris, Malygos had been able to direct powerful surge needles, using them to pull arcane magic from Azeroth's ley lines and channeling that magic into the Nexus.[1] The slain Arygos' blood was used by Aedelas Blackmoore to use a surge needle (with energies flowing from the Nexus) to animate Chromatus.[2]
The Demon Soul
As part of the Dragon Soul raid introduced in Patch 4.3, adventurers have to get the Focusing Iris so the Dragon Aspects can refocus their power into the Dragon Soul to use the Demon Soul artifact against Deathwing.[3]
Notes
It was previously mentioned that once harnessed, the energies are focused through the Nexus' ascending rings and blasted into the Twisting Nether.[4] In Thrall: Twilight of the Aspects, this function of the Nexus is not mentioned. It is implied that energies are stored there.
Patch changes
Patch 4.2.0 (2011-06-28): No longer requires 
[Key to the Focusing Iris] or [Heroic Key to the Focusing Iris] to activate. - Patch 3.0.3 (2008-11-04): Added.
