Unique Active - Stasis: Put yourself in stasis for 2 seconds, rendering yourself untargetable and invulnerable for the duration, but also unable to move, attack, cast spells, or use items during this time. 90 second cooldown.
It was broken up into two different items, Zhonya's Hourglass and Rabadon's Deathcap, in V184.108.40.206. Zhonya's Hourglass was given the 2.5 second invulnerability active (defensive aspect), while Rabadon's Deathcap was given the ability power passive (offensive). The reason for Zhonya's break-up into two items was because the item "gave ultimate offense and ultimate defense for casters" which was deemed too strong.