We don't like those pesky casters, do we?

The following is my favorite mesmer / elementalist build. I mostly played in the 4v4 random arena, so that's where it is most effective.

Attributes:

7 - Fast casting
7 - Illusion magic
14 - Domination magic
10 - Earth magic

Skills (from left to right):

1. Energy Surge [elite]
2. Energy Burn
3. Backfire
4. Obsidian Flame
5. Resurrection Signet
6. Illusion of Weakness
7. Hex Breaker
8. Armor of Earth

The weapon of choice is a domination staff with +60 health.

The runes are minor runes, except for the superior vigor rune.

The headpiece is +1 domination.

How to play this build:

Cast Illusion of Weakness and Hex Breaker on yourself, and run to the enemy. Choose and call the target. Before getting in their aggro circle, cast Armor of Earth. Then - Backfire, Energy Surge, Energy Drain, Obsidian Flame. Spam Hex Breaker as soon it disappears. As soon as someone dies, resurrect with your signet.

This build got pretty much everything you need: fun and powerful spells, messing with the enemy, killing the enemy outright, and decent survival.

There is no need for a superior domination rune, as two extra points won't help Energy Surge and Energy Drain. You could, however, use those two points and put them into Earth Magic to help Obsidian Flame a bit. In general, as I'm usually the first one to run in and get targeted, I found the 75 health to be more useful.

The best thing is that the spells are damage dealers which ignore armor, so after you finish off the casters, the warriors go down as well.

This is quite a balanced build, so you can use it in PvE as well (just don't use Obsidian Flame when you don't have to, it takes long to recover max energy if you deplete it completely).

Have fun!