How many times can dancing double weapons attack?

Question

Let's assume my character has 6 BAB. He can make two attacks per turn with a basic one handed sword.

His wizard friend wants to create an Urgrosh with the dancing property. As far as I know, dancing weapons use their owner's BAB, so they can perform iterative attacks.

However, an Urgrosh has a special property called "double". It means they can be used as two weapons when it comes to two-weapon combat rules.

Here are my questions:

• Does it mean a Dancing Urgrosh can attack three times per round when it flies above my character's head?
• If so, how about the penalties? My character has the Two-Weapon Fighting feat.

I didn't find anything useful in that regard in the dancing dancing property rules:

As a standard action, a dancing weapon can be loosed to attack on its own. It fights for 4 rounds using the base attack bonus of the one who loosed it and then drops. While dancing, it cannot make attacks of opportunity, and the activating character it is not considered armed with the weapon. The weapon is considered wielded or attended by the activating character for all maneuvers and effects that target items. While dancing, the weapon shares the same space as the activating character and can attack adjacent foes (weapons with reach can attack opponents up to 10 feet away). The dancing weapon accompanies the activating character everywhere, whether she moves by physical or magical means. If the activating character has an unoccupied hand, she can grasp it while it is attacking on its own as a free action; when so retrieved, the weapon can’t dance (attack on its own) again for 4 rounds. This special ability can only be placed on melee weapons.

Answer 1

Double headed magic weapons are (sort of) two magic weapons

As stated in the section on Creating Magic Weapons (p551 of Core Rulebook):

Creating magic double headed weapons is treated as creating two weapons when determining cost, time and special abilities.

In many ways this is the way double-headed weapons are treated in combat - there is very little mechanical difference between wielding a two-bladed sword and wielding two longswords (except that the other end of a double headed weapon is considered to be "light"). So when the rules state that "As a standard action, a dancing weapon can be loosed to attack on its own", one interpretation is that this applies to only one head of a double headed weapon. The other head of the weapon is only along for the ride, so to speak.

As a corollary, it is not possible to set both heads of a double headed weapon dancing, because in order to "loose" the second head the weapon would have to be grasped again, which would end the first head's dance.

While this interpretation may (correctly) be seen to make a dancing double headed weapon rather less useful, it is probably better than the alternative given that the only bonuses that apply to a dancing weapon are BAB and the weapon's enhancement. Spells and abilities that allow attribute bonuses, feats and other abilities to be applied explicitly state this, for example the Bow Spirit spell states:

The bow spirit uses your base attack bonus plus your Dexterity modifier, as well as any bonuses and effects from feats you have that affect ranged attacks, or bonuses from the ammunition it uses.

As the description of the dancing property omits any mention of the feats, attributes etc of the character that "loosed" it to "attack on its own", if attacks with the second head were allowed then there would be penalties of -4 on the primary head attacks and -8 on the secondary head attacks.

Note that the answer to this question provides a different interpretation of the exact bonuses on the dancing weapon's attacks - personally I would not include modifiers for the size of the dancing weapon as an object, but that is a separate question.

TL:DR - the wizard only needs to enchant one head of the urgosh to be dancing, but it will only make two attacks per round - one at +6 + dancing head enhancement, the second at +1 + dancing head enhancement. However, the rules are unclear and other interpretations are possible.

Answer 2

I believe that both heads would have to have the dancing property for this to work.

Each head of double weapons has to be enchanted separately and do not share enchantments.