A warforged component usually occupies the same space on the body that a magic item of the same kind normally would.
Eberron Campaign Setting pg. 268
Battlefist (attached component): This +1 weapon resembles a massively oversized spiked gauntlet; one designed for a Medium warforged looks like a gauntlet designed for an ogre. It attaches to the arm of a warforged, completely covering the hand.
Eberron Campaign Setting pg. 268
So a battlefist should be treated as a Large +1 spiked gauntlet. That much is easy. Let’s get some other easy stuff out of the way:
Yeah, ogre-sized implies a Large item. Not really relevant to the question.
So does a Large +1 spiked gauntlet use the arms slot?
Definitely not; gloves, gauntlets, and the like are hands-slot items. See Magic Items on the Body:
- One pair of bracers or bracelets on the arms or wrists
- One glove, pair of gloves, or pair of gauntlets on the hands
The battlefist is “of the same kind” as a +1 spiked gauntlet, which definitely is more like “One glove, pair of gloves, or pair of gaunlets” than it is “One pair of bracers or bracelets on the arms or wrists.” So the arms slot is definitely not involved.
Is it even physically possible to wear gloves or gauntlets with a battlefist?
Physically covering the hand does not necessarily mean that you cannot use other items—gauntlets and gloves can be sized to fit under the battlefist or over it, and magic gauntlets and gloves will (usually) resize to do one of these things.1
Even if the battlefist does physically interfere with a particular magic gauntlet, it should be possible (assuming that gauntlet isn’t an artifact or something) to get the same magic on a pair of gloves or similar that the battlefist won’t cause physical problems with.
But will the battlefist magically interfere with hands-slot items?
Not at all, in my opinion, but the rules get murky here; we have left the land of easy answers. The rules for gauntlets and spiked gauntlets are a mess, as our myriad questions on the subject can attest.
The issue is a distinction apparent in the rules but not explicitly described by the rules. Usually, magic weapons and worn magic items are completely different, and use different rules. There’s no such thing as a “weapon slot,” the way there are the hands slot and the arms slot and so on. You can use multiple magic weapons at the same time without the magic interfering; if you want to hold a +1 dagger in a hand wearing a +1 spiked gauntlet, you can stab them or punch them and each attack is going to benefit from the +1 enhancement on the corresponding weapon. If you wear gauntlets of ogre power +2 over gloves of dexterity +2, the magic interferes with one another, so only one applies.
And you can certainly use a +1 dagger in a hand wearing gauntlets of ogre power +2 without any problems with either the enhancement bonus on attacks and damage and the enhancement bonus to Strength.
Moreover, gauntlets of ogre power +2 and gloves of dexterity +2 are created using Craft Wondrous Item; a +1 dagger or +1 spiked gauntlet is created using Craft Magic Arms & Armor.
So magic weapons and worn magic items are separate and do not interfere with one another. Now what happens when you worn item is a weapon, or your weapon is a worn item—as in the case of gauntlets, spiked or otherwise.
If you punch someone with gauntlets of ogre power +2, you should use the stats for a gauntlet, that much is clear. But do you get any enhancement bonus on the attack or damage? No, you don’t, because the +2 enhancement bonus to Strength is not any kind of weapon enhancement. Does it count as a magical attack? Again, no, it does not, because a magic attack requires weapon magic. This is similar to bashing someone with a +1 heavy shield—that +1 enhancement to the shield’s AC does not apply to its bashing capabilities. For shields, this is explicitly stated. For gauntlets, not so much—we got little and less detail on gauntlets in general, as already established by my little list of other questions.
But let’s take a look at that explicit description for shields:
An enhancement bonus on a shield does not improve the effectiveness of a shield bash made with it, but the shield can be made into a magic weapon in its own right.
Heavy shield description, light shields and shield spikes have similar descriptions
Note the “but the shield can be made into a magic weapon in its own right.” Being a magic weapon is priced and limited completely independent of being a magic shield.2 The weapon magic and the shield magic operate independently, despite being on the same physical item.
This establishes, again, that magic weapons are their own thing, separate from other kinds of magic items. A pair of +1 spiked gauntlets is enhanced as a pair of weapons—not as worn items. They’re made with Craft Magic Arms & Armor. To be consistent with the precedent set by shields, if they were also a pair of gauntlets of ogre power +2, the cost of the gauntlets of ogre power +2 would not be affected by the cost of the +1 weapon enhancement, nor would the +10-enhancement-equivalent or 200,000 gp limit on magic weapons be affected by also being gauntlets of ogre power +2.
All of which is to say that it is the hands-slot magic that occupies the hands slot. Something crafted with Craft Wondrous Item, providing a passive, non-weapon benefit. The battlefist doesn’t have that, by default. It could, presumably, since it is a gauntlet and could get extra magic like one, but by default it’s an oversized +1 spiked gauntlet. That’s weapon magic. It shouldn’t interfere with worn-item magic.
Ultimately, the battlefist does not mention the hands slot or that you cannot use hands-slot items while using it. Neither do the weapon descriptions for gauntlets or spiked gauntlets. And I like to think that if it blocked those items, that would be mentioned.
Whether or not and how magic items resize is not given a lot of definition under the rules and is largely left up to the DM, but the rules do say that “most of the time” sizing “shouldn’t be an issue.”
Pathfinder questions, but the rules didn’t change between D&D 3.5e and Pathfinder.