In our Pathfinder game, we recently came upon a Sword of the Planes.
This longsword has an enhancement bonus of +1 on the Material Plane, but on any elemental planes its enhancement bonus increases to +2. The +2 enhancement bonus also applies whenever the weapon is used against creatures native to the elemental planes. It operates as a +3 longsword on the Astral Plane and the Ethereal Plane, or when used against opponents native to either of those planes. On any other plane, or against any outsider, it functions as a +4 longsword.
We initially interpreted this weapon (when used on the Material plane) as being a +1 weapon normally, +2 against elementals, +3 against creatures from the Astral or Ethereal Planes, and +4 against other outsiders. We weren't sure about what it would do to native outsiders, so we deferred that decision.
However, a second reading of the rules says that it is +4 against any outsider, not any other outsider. This seems odd, since there are only a few creatures native to the elemental, Astral or Ethereal planes who aren't outsiders.\$^1\$
What is the correct reading of the rules? Does the Sword of the Planes have a +4 bonus against literally any outsider, or just any outsider not covered by the rest of the description? And is one interpretation more balanced than the other?
1: Searching for non-outsiders, I have found Astral Dragons, Devourers and Ouroboros in the Astral Plane, Cloud Dragons in the Plane of Air, Crystal Dragons in the Plane of Earth, Magma Dragons and Fire Whales in the Plane of Fire, Brine Dragons, maybe some Merfolk, maybe some Sahuagin, possibly some Scyllas (by random encounter table) and possibly some Krakens (by random encounter table) in the Plane of Water, and Phase Spiders, Thought Eaters, maybe Ectoplasmic Creatures, Nightmare Dragons, Etheric Dragons and Dream Dragons in the Ethereal Plane. Admittedly, this list is less small than I first thought, although the majority of the occupants of a foreign Plane are still outsiders.