Causes an explosion of shadow magic around the enemy target, causing [(25% of Spell power) * 5] Shadow damage every 1 sec for 5 sec to all enemies within 10 yards around the target.
Mind Sear is a priest ability learned at level 28. It is an AoE base ability that can be cast upon an enemy or friendly target; it will damage all enemies within range, including the targeted enemy (not the friendly target, however). This is a high aggro/threat attack, so be careful to not pull too many mobs with it.
This cannot be self-cast on the priest, nor on non-combat pets.
It is useful to use this spell on the main target in a raid. If there are a bunch of mobs, you should put DoT's and use this spell on the main target of other DPS's so you can damage the main target while you deal damage to other ones too.
In PvP, this is useful anywhere there is a group of enemies. Though, it can also be used to find out Stealthed enemies under some circostances. For example, let's say there is a Stealthed Rogue near another player of his same faction, you can use this spell on the visible target and catch out the Rogue.
In Arena PvP, this is useful to damage enemies that are behind pillars. If you are against a Shaman for example, he stays behind a pillar not in LoS, but he puts a totem on the ground and it is in Line of Sight (I.E. attackable) You can use Mind Sear on the totem to damage the Shaman.