Secondary professions for an Assassin

Assassin/Warrior
Due to their base attack speed, Assassin/Warriors get a lot of adrenaline, so it's possible to use adrenaline skills to great affect. Skills such as Rush or "Fear Me!" are good examples: while attacking a target, you can continuously Rush. Fear Me is a great energy drain, but it requires investment in Tactics to yield results.

Also, the Assassin's primary attribute Critical Strikes can be useful when wielding an axe or another Warrior weapon. The sheer damage of a Warrior weapon with a high chance of critical strikes amount to a ferocious combination. Axes and Hammers may be the best choices in this case; they both have a big high-end damage, which affects the critical hit damage. Axes allow for a shield off-hand, and attack faster. Also, Axe Mastery has more skills that attack more than one opponent. Hammers, on the other hand are two-handed weapons and thus deny the use of shields, which precludes the potential armor and health bonuses from a shield but spares the attribute point cost of meeting a shield's requirement.

Assassins do not have any attack speed enhancing stances, and can thus greatly benefit from Warrior skills such as Flurry and Burst of Aggression. Burst of Aggression can be particularly useful, as it has no negative drawback for its speed boost other than the loss of adrenaline, which Assassins do not often use.

Example Builds:
 * Build:A/W Critical Mastery

Assassin/Ranger
The Assassin Ranger, like the Warrior Ranger, yields many good skill combinations. Ranger is a particularly versatile class, and the Assassin primary can benefit from this.

Skills like Troll Unguent could supply some healing to the class, and a pet can help the Assassin absorb more damage, although the 8 sec skill recharge when a pet dies can kill an assassin easily.

You can also use Tiger's Fury to boost your damage output. There is also an Assassin skill, Exhausting Assault, which causes interruption and exhaustion; combined with the Factions skill Equinox (which doubles exhaustion in the area), the A/R could lock down spell casters.

Apply Poison, with a poisonous dagger mod, is a boon to the assassin. This can be effective in PvE when combined with AoE skills such as Death Blossom.

Barrage damage can be improved with high critical strikes attributes, adding bonus damage to attacks, energy bonus, and effects from skills like Way of Perfection. Example Builds:
 * Build:A/R Critical Barrager
 * Build:A/R Solo Rajazan's Fervor Farmer

Assassin/Elementalist
As there is a weapon upgrade that can convert the damage on an Assassin's primary weapon, namely daggers to lightning damage, use of the skill Glimmering Mark with this upgrade will allow the assassin to greatly lower vulnerability against Warriors and other Assassins.

Another option would be to take several close quarter spells of a single element with you (like Shockwave and Aftershock) allowing you to deal a lot of damage to nearby enemies. You could also use their weapon enchantments to boost your overall damage output.

You can also use Earth Magic skills to boost your armor and create wards to negate damage before it happens. The energy cost can often be prohibitive at lower levels, or high death penalty, however.

Another possibility is to use the Shrouded armor set, and utilize critical strikes and elemental hexes to debilitate foes. The skill Black Lotus Strike grants the user energy upon a successful strike, and can go directly into Twisting Fangs, thus doing an enormous amount of damage. With water hexes such as Blurred Vision, the warrior and assassin threat may be mitigated, and using possibly Mirror of Ice, threats from high-damage spells can be turned against foes.

Example Builds:
 * Build:A/E Falling Shocker
 * Build:A/E Signet Spiker

Assassin/Mesmer
The Mesmer skill Blackout can be used while all of your attack skills are recharging without penalty, and can also be employed in combination with Temple Strike to further lock down a foe. Illusionary Weaponry along with the Assassin's fast attack speeds can work for a high damage combo.

Distortion makes for a very effective defense skill when combined with the energy regeneration effect of points in Critical Strikes. Also, Physical Resistance and Elemental Resistance can boost an Assassin Mesmer's armor to levels comparable to that of Warriors.

Since dagger attack skills often cause conditions, Fragility is a good way to do extra damage to your target. In case of multiple targets, Epidemic can be used to spread those conditions.

An Assassin Mesmer can gain an advantage against other melee classes with Empathy and can be more effective against Monks with Backfire.

The Assassin Mesmer is excellent at running, especially with a buddy; with a 20% enchantment item and full attribute points in Shadow Arts, Shadow Form coupled with Arcane Echo and if with a friend, Arcane Mimicry, can produce a mostly unstoppable force.

Channeling is also useful for builds which frequently use Deadly Arts or Shadow Arts spells.

Example Builds:
 * Build:A/Me Solo Sin

Assassin/Monk
Using the offensive spells Smiting Prayers of the Monk can enhance the offensive effectiveness of a melee Assassin. In particular, one could use Bane Signet which provides a knockdown effect and follow that up with a Falling Spider combo.

The Protection Prayers skill Mending Touch is a good spell to remove risky conditions.

One might consider using Vigorous Spirit and Live Vicariously of the Healing Prayers line, as the Assassin is able to generate a high amount of hits per second. Healing Breeze is also a solid choice.

Two other skills that the Monk brings to the table are the very popular Rebirth, which is often much better than Resurrection Signet in PvE, and the very handy Purge Conditions, which will allow the assassin to shake off nasty conditions such as blindness, bleeding and poison.

Assassins generally have trouble finding groups, and Assassins with Monk secondary even more so, since some players might assume that an Assassin with good healing capabilities is even less likely to play 'hit and run' than the average Assassin and just use the healing to try to tank better/longer.

Example Builds:
 * Build:A/Mo Enchantment Assault

Assassin/Necromancer
Combining Necromancer and Assassin teleport skills as well as Necromancer touch skills coupled with a dagger, the A/N is an effective hit-and-run build. The Assassin skill Death's Charge teleports to an enemy and heals, which can quickly be followed by Vampiric Touch, resulting in great health gain. Assassins can increase their consistent damage through the use of skills such as Barbs, Mark of Pain, and Weaken Armor. Rigor Mortis may be used as a longer-lasting alternative to Expose Defenses to guarantee that chained dagger attacks find their mark. Another useful combo is Spinal Shivers/Shivers of Dread coupled with a set of cold damage daggers. Although you may lose a lot of energy this way, the fast attack speed of Assassins guarantees interruption of almost every skill the enemy uses.

Furthermore, the Necromancer skills Plague Touch and Grenth's Balance require no attribute investment, and both have handy effects for melee fighters. The use of these two skills exclusively from Necromancer means you can freely spend all your attributes on Assassin.

Example builds:
 * Build:A/N Repeating Moebius

Assassin/Ritualist
A popular PvE combo as it allows Guild Wars players to fight through the Factions storyline only once and unlock the skills for both new professions. This character can employ spirits before it engages and can then proceed into melee with a distinct advantage. Ritualist weapon spells, such as Brutal Weapon, can also add significant damage to Assassin attacks, and is especially effective due to the Assassin's attack speed.

An Assassin can also utilize the Ritualist secondary for assistance skills such as Generous Was Tsungrai for healing, Resilient Was Xiko for condition removal, or Flesh of My Flesh for resurrection. By placing a spirit in a safe place before you engage foes, you can Shadow Step back to it, using Spirit Walk.

Assassin/Paragon
The Assassin may use the Paragon second profession by giving the class much needed protection from damage. This may help the fact that the Assassin has relatively low armor and is considered a "soft target". By using the Paragon's various shouts, it also may help improve damage output, which would make the Assassin an even faster killer. For example, the Paragon skill Go for the eyes is a spammable adrenaline skill that can help the Assassin (and teammates) land more critical hits.

Assassin/Dervish
In the same fashion as the A/R Critical Barrager, the Assassin Dervish could use his skills to greatly improve Critical Hit chance with his scythe. Despite having a huge damage range compared to other weapons, the Assassin's Critical Strikes attribute can increase the chance of critical hits occuring, and when coupled with the Scythe's maximum damage, can result in massive simultaneous damage while gaining energy.

Example Builds:
 * Build:A/D Disciple of Death