This build relies on the Mesmer's primary ability of Fast Casting, combined with the power of Auspicious Incantation and Echo, to produce a quick spike of highly damaging Fire Magic spells and superior energy management.
Fast casting reduces the amount of time required for casting spells according to the following formula: (Cast time) = (base time)/(2^(attribute/15))
This means that with Fast Casting of 15 all spells cast 50% Faster.
Fast Casting: 11 + 1 + 3
Inspiration Magic: 6 + 1
Fire Magic: 12
Enchanter's or Radiant armor for the extra energy.
In addition to the Fast Casting and Inspiration runes, use the best Vigor rune you can afford and an Attunement rune on the chest and legs.
Use a +15/-1 energy Fire Wand with a 20% chance to halve the recharge of Fire Magic spells and a +15/-1 with +12 energy Flame Artifact (such as the Fire Wand and Articfact crafted by Honglei Sun in Matuu Keep)
Swap to another weapon set when gain the extra 2 pips of energy regeneration. Make sure to use a staff or wand and offhand with fire attibute HSR 20%.
Lava Arrows fly toward up to 3 foes near your target and strike for 20..56 damage if they hit. Lava Arrows have half the normal range.
Send out a ball of fire that strikes target foe and all adjacent foes for 7...91 fire damage.
Mark of Rodgort
Target foe and all nearby foes are Hexed with Mark of Rodgort. For 10...30 seconds, whenever each foe is struck for fire damage, that foe is set on fire for 1...3 seconds.
Target foe and all nearby foes are struck for 15...99 fire damage and set on fire for 1...3 seconds.
For 20 seconds, the next Spell you use is disabled for an additional 30 seconds and you gain Energy equal to 110...182% of that spell's Energy cost. The recharge for Auspicious Incantation is reset, and it has an additional recharge time equal to that Spell's Energy cost.
Using this on a Echo-duplicate spell allows you to bypass part of this skill's drawbacks.
For 30 seconds, Echo is replaced with the next skill you use.
Create a Meteor Shower at target foe's location. For 9 seconds, foes adjacent to that location are struck for 7...91 fire damage and knocked down every 3 seconds. This Spell causes Exhaustion.
For 36...55 seconds, you are attuned to fire. You gain 1 energy plus 30% of the energy cost of the skill each time you use Fire Magic.
Keep Fire Attunement up at all times, without it energy management becomes very difficult.
When facing small mobs cast Mark of Rodgort, Echo and Fireball, then spam Fireball and Lava Arrows consistent damage and burning. When you get down to 30 energy cast Auspicious Incantation followed by Rodgort's Invocation. This should Max out your energy bar. Auspicious Incantation and Rodgort's Invocation will be disabled for 50 and 45 seconds.
When facing a large mob cast Echo, Meteor Shower, Rodgort's Invocation, Auspicious Incantation and finally the Echoed Meteor Shower - at the end of this chain you will have a full energy bar of around 50 (due to the energy lost to exhaustion). This allows you to keep Meteor Shower up for 18 consecutive seconds, and immediately follow it up with Mark of Rodgort and then spam Lava Arrows to cause damage and Burning.
Auspicious Incantation can be swapped for Glyph of Lesser Energy. This makes the build easier to run at the cost of a slight reduction in energy management capabilities.