General Principle

IW allows the caster to do a respectable amount of melee range damage that cannot miss or be blocked. IW is peculiar in that its damage replaces melee attack damage. In so doing, it allows the caster to use any melee weapon regardless of its attribute requirement. IW damage does not count as an attack and will damage an opponent even when the caster is blind or the opponent would otherwise block an attack. Traditionally, the IW mesmers use attack speed increasing skills such as Flurry to do higher DPS since they are not affected by Flurry's damage reduction.

Side Skills

Illusion of Weakness is sometimes paired with IW mesmers as a cover enchantment. Its utility is that it does not expire unless the player loses a significant amount of health. It's also not uncommon to use defensive assassin skills (Dark Escape and Feigned Neutrality don't expire from this enchantment's damage). Energy management and interrupt skills such as Leech Signet and Power Drain are also sometimes taken to keep Flurry going and to prevent enchantment removal. Distortion is also used to avoid damage on the front line.

Although rarely seen, combining the IW mesmer with the basis of the 55 monk build can be rather effective, but because of the high reliance of Protective Spirit, you are limited in where you can solo farm. The most common place is outside Augury Rock because the Hydras do not have a self-heal, Although they are high damage dealers, thanks to Protective Spirit, the damage should only be 5 from each hit or spell. Watch out for their interrupt in the beginning though.

Equipment

IW only works with melee weapons. People mainly use swords or axes because of the faster attack rates over hammers. At the cost of losing a slot for a shield or focus item and lower attack rate, one could use two handed weapons. Daggers are mainly used against single enemies, due to the chance of striking twice. Scythes are more commonly used against mobs, for they have the ability to attack up to three foes at once. Since IW does fixed damage, the damage statistics and weapon requirements are negligible. Also, most IW mesmers have their weapon upgraded with a +20% enchantment mod to lengthen the durations of their enchantments.

Armor is rather strict. As being a caster, mesmers will need an abundant supply of energy. So, players sometimes add radiant insignias and runes of attunement. It is not uncommon to use runes of vigor to increase maximum health. Runes of purity, recovery, and restoration may be used to reduce the amount of time the mesmer is under certain conditions. The rune of clarity is never or rarely used, since IW ignores the effects of Blind and the damage reduction (but not attribute reduction) of Weakness.

Battle Behavior

There are at least three different ways to play the Illusionary Weaponry Mesmer.

The first is to play as a frontline melee fighter. The skills provided in Illusion Magic can be very effective when used against enemy melee in combination with Illusionary Weaponry. You can block an opponents strongest melee attacks with Distortion, and then counterattack with Flurry + Illusionary Weaponry. You can also open combat with various hexes, making your opponents die much faster through degeneration, or making yourself next to invincible (Spirit of Failure + Distortion is very good for this). The most important thing when using this style of play is to correctly choose when to use Distortion and when to use Flurry, as both are stances and will replace each other. Not using Distortion when you need to can get you killed instantly, as Mesmers have little armor to protect them. By far though, this option's strongest weakness is enchantment removal. Once a Necromancer with Strip Enchantment realizes what you're doing, you may as well resign. You will be virtually harmless without Illusionary Weaponry.

The second option is to play as you would normally play an Illusionist Mesmer, only brandishing Illusionary Weaponry when an opportunity presents itself. This playstyle allows you to be very effective both as a spellcaster and a melee combatant: extensively weakening your opponents through degeneration, and then cutting them down from their weakened state. This option also defeats the weaknesses of the first, as you are still a serious threat without your melee strength. Also, if you are dealing with enchantment removal, you will find that you are often able to kill your target in the few seconds before the enchantment is removed. Keep in mind, though, that if you choose to play this way you are no longer capable of frontline combat. You will be forced to replace your defensive skills with energy management skills and a stronger arsenal of degeneration hexes.

The third option is to combine Domination Magic with your melee attacks. This option will allow you to achieve a balance between the first two styles of play. You will have room for some defensive skills, while still having a secondary weapon in Domination Magic. You can also take various interrupts with you, allowing you to block enchantment removal spells.

Disadvantages

-The largest flaw of this build is that it relies so heavily on one enchantment for damage. If the cornerstone enchantment is removed, the build will have very little damage output left. If the enchantment is removed as soon as it is cast, the mesmer must wait close to 25 seconds before being able to deal much damage again.
-Constant use of Flurry and Enchantments can drain the energy out of IW mesmers pretty fast.
-Mesmers have a low armor rating and making them a frontline character is risky because they can fall very quickly when targeted unless they are using the 55 monk build in correlation with IW mesmer (in which armor doesn't matter, the damage would be the same.)
-Any hex that slows attack speed will also hurt this build considerably.
-The lack of any kind of real utility makes IW Mesmers worse than any traditional frontliner.
-The amount of DPS mesmer produces is barely comparable to that done by any weapon class, however, it can bypass blindess and blocking.


Information from wiki.guildwars.com