Do Properties of magic weapons stack when using Two-Weapon Fighting?

Question

Let's assume my monk has the Two-Weapon Fighting feat.

1.) When I use two daggers, one with Ki-Weapon and another magic dagger, do the magic features of the Ki-Weapon and the magic dagger stack?

It says so in this forum thread:

There is no effect at all of having a second weapon. If you have Two Weapon Fighting then it adds +1 damage to your primary attacks. The only real effect is that you can switch between the weapons whenever you want and you can gain the benefits of the magic abilities of both.

...but I can't really imagine this is true because this could be pretty strong.

2.) If so, would it be possible to use a Ki Focus and two magic weapons then, stacking properties and powers from three places?

Answer 1

It depends on the magic items in question.

It doesn't matter how many weapons or implements you equip/wield, you can only use 1 weapon or implement (the ki focus can be used through a weapon, but this counts as using the ki focus and not the weapon) on an attack.

Enhancement bonuses from multiple weapons or implements do not stack; only the enhancement bonus of whatever you use for the attack is added. The feat Dual Implement Spellcaster allows you to add a bonus equal to a 2nd implement's enhancement bonus to damage on arcane powers, but that's about the only way around this limitation.

Other properties may stack depending on how they're phrased. If the item's property says something along the lines of "when you attack with this weapon" then it can only be used when that's what you're attacking with. If the property has no such restriction then you get the benefit even when you attack with something else, though relatively few such properties are related to attacks.

Note that the Two Weapon Fighting feat has nothing to do with any of this. Any character can wield 2 one-handed weapons this way. That feat has nothing to do with magic items. Further, Two Weapon Fighting only adds its bonus to weapon attacks, which monks don't usually make.

Answer 2

A) Two-Weapon Fighting mostly has no effect on a Monk. It only applies to Weapon attacks, and Monks have none of those.

B) Weapons in your other hand do not affect your attacks, as described in the Adventurer's Vault page 56:

Weapon Properties: Many weapons have properties that provide a constant benefit. To gain the benefit of a weapon’s property, you must be wielding the weapon. Unless specified otherwise, a property affects only the weapon to which it’s attached.

So Vanguard only applies if you attack with that weapon. Actually, every weapon property should be read as "if you attack with this weapon", if it makes sense. So non-attack properties and powers are legal.

For example Weapon of Defense gives you resist all 1 when you hold it, because this property is not connected to attacking.

C) Implements do not fall under the above mentioned rule. Rain of Hammers is such a popular utility (as in not-attacking) ki focus because its property triggers no matter what you use to kill that enemy. Weapons used as implements (like heavy blades for Swordmasters) are still Weapons and are included in the rule.

As Oblivious Sage pointed out there are some ways to add damage from the off-hand weapon, the Dual Implement Spellcaster is one prominent example, but it is not really good for a Monk as it has no Arcane powers. You can get some with Hybrid or Multiclass, but it is far from optimal.

In conclulsion: Weapons in your off-hand can be really valuable, but not in attacking. They can increase your Shield bonus (Rhythm Blade), or improve your Initiative, or many other thing however.