Timbal's Focusing Crystal

Source
Dropped by Priestess Delrissa in Magisters' Terrace (Heroic mode).

Functionality
This trinket gives a chance to deal extra damage in the form of a Shadow Bolt, which is capable to do a spell critical strike, at every tick of a DoT or channeled spell. It seems to work with any DoT and channeled spell placed on the target, including AoE effects.
 * Note: The proc has a hidden cooldown of 15 secs.

Works with Druid - Entangling Roots, Hurricane, Insect Swarm, Moonfire Mage - Fireball, Flamestrike, Ignite, Pyroblast Paladin - Consecration, Seal of Vengeance Priest - Holy Fire, Mind Flay, Shadow Word: Pain, Vampiric Touch Shaman - Flame Shock Warlock - Corruption, Curse of Agony, Drain Life, Drain Soul, Hellfire, Immolate, Rain of Fire, Seed of Corruption, Siphon Life, Unstable Affliction

It should also work for a hunter's Serpent Sting, Volley, and maybe Explosive Trap and Immolation Trap, but hunter's would find little other use in this trinket, as those are minor abilities and they don't need spell damage.