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 Truth
 * Priest - Holy Fire, Mind Flay, Shadow Word: Pain, Vampiric Touch
 * Shaman - Flame Shock
 * Warlock - Corruption, Bane of Agony, Drain Life, Drain Soul, Hellfire, Immolate, Rain of Fire, Seed of Corruption, Unstable Affliction

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