Chaos Storm

Acquisition
Skill Quests: Skill Trainers who will teach this skill before it is unlocked:
 * Trying Times (Sardelac Sanitarium)
 * Captain Osric (Yak's Bend)
 * Dakk (Ember Light Camp)

Usage Notes
This is the Mesmer's staple area of effect damage skill. It creates a Chaos Storm (which looks like a bunch of swirling purple circles) around whoever your target is when you cast it. It will hit all foes adjacent to the location it is cast.

In PvP this skill is useful in a few different situations, such as when a few enemy casters decide to stay in a group. Throw this near them and they will be forced to move away. Also, although perhaps not as efficient, Chaos Storm can be used in the primary battle between Warriors. Its energy draining side effects won't be realized, but as Warriors fighting each other don't tend to move around too much it is more likely that this skill will output its full damage. You can also cast Chaos Storm on an attacker who is targeting you at melee range. This will severely damage and drain the foe, or force that player and other enemies to stay away from you.

In PvE Chaos Storm is useful to hurt and disrupt groups of enemy spellcaster standing in clusters. However, note that the spell will be detected as AoE damage by the enemy AI, so foes will try to move out of the range of effect. Skills that slow movement speed can be useful here.

Because of Fast Casting and its short cast time, it is also effective in PvP as a way to punish casters who use spells with high mana costs and long cast times. An elementalist hit by Chaos Storm shortly after starting to cast Meteor Shower for example, may choose to wait through the casting rather than cancel the spell to escape the storm. After two or three seconds of storm damage and mana drain, they can still be hit with an interrupt before they finish casting for further punishment.

The primary drawback to the skill is its weighty 15 energy cost. Skills like the Elementalist Glyph of Lesser Energy can help greatly.