Shadow Orbs

Shadow Orbs are a unique Shadow priest resource displayed in the user interface beneath the player's health and mana bars. They become available to Shadow priests at level 21.

Shadow Orbs are generated by Mind Blast and Shadow Word: Death. They are used to cast Devouring Plague and Psychic Horror.

Priests can have a maximum of 3 Shadow Orbs at a time, or 5 once Enhanced Shadow Orbs has been acquired. Psychic Horror will consume up to 3 Shadow Orbs, empowering the spell according to the number consumed, requiring a minimum of 1 Shadow Orb; while Devouring Plague always consumes 3 Shadow Orbs, and cannot be cast with fewer.

Shadow Orbs do not decay or disappear over time; they can be stored indefinitely until they are needed. However, events such as dying or logging out will reset the priest's Shadow Orbs.

Improvements
Talents, abilities and glyphs that increase the availability of abilities that generate Shadow Orbs can in turn lead to increased Shadow Orb generation. Examples include Divine Insight and Glyph of Shadow Word: Death.

Tips
Any Orbs generated while at the maximum will be wasted. Priests with full Orbs should generally therefore try to make use of an ability to consume them, before using abilities that will generate further Orbs.

A simple tactic to provide an edge when facing a tough opponent is for the priest to first generate 3-5 Shadow Orbs from fighting other, usually weaker, foes, before engaging the more challenging target. As Shadow Orbs can take some time to accumulate (especially in single combat), this tactic can substantially increase DPS in short encounters.