Area of Effect (AoE) skills affect a given area of the playfield, and not any one specific target; any target inside of the area will be affected by the skill. The affected area generally does not move over time, so players can move away to avoid negative effects or closer to benefit from positive effects. Area of effect skills affect all valid targets within the horizontal radius regardless of barriers or altitude.
In PvE, since the 2005/11/10 update, henchmen and creatures flee from AoE skills that do damage over time, but generally take 2-3 seconds of damage before fleeing.
Most AoEs require a target; however, some will take effect around the caster. These are called PBAoEs—point-blank area of effect.
See also: Range
Body-Blocking Trick
As stated above, computer-controlled creatures will flee upon being inflicted with such pulsing damage after two to three seconds. However, if the creature is effectively body-blocked by players or any other mobs (not including spirits), it will be mind-frozen trying to reach its previous target or skill use location: hence a melee or touch-range Boss could be defeated easily, unable to attack or use any offensive abilities.