Specifically looking at this ability:
Spirit Totem, Lesser (Su): While raging, the barbarian is surrounded by spirit wisps that harass her foes. These spirits make one slam attack each round against a living foe that is adjacent to the barbarian. This slam attack is made using the barbarian's full base attack bonus, plus the barbarian's Charisma modifier. The slam deals 1d4 points of negative energy damage, plus the barbarian's Charisma modifier.
Can the barbarian count themselves as an adjacent foe? First, is a combatant considered adjacent to themselves? Second, can they consider themselves a foe for a specific ability? Lastly, can the combatant choose to be hit by this ability in some way (flat out get hit, deny DEX bonus to AC, or treat themselves as helpless for the purposes of the attack)?
Related question to adjacency:
Are two creatures in the same square adjacent for purposes of feats/abilities? (let's assume they're both Tiny or Diminuitive for that one)
is a combatant considered adjacent to themselves?
and
Are two creatures in the same square adjacent for purposes of feats/abilities? (let's assume they're both Tiny or Diminuitive for that one)
Tiny, Diminutive, and Fine Creatures: "Creatures that take up less than 1 square of space typically have a natural reach of 0 feet, meaning they can't reach into adjacent squares. They must enter an opponent's square to attack in melee... You can attack into your own square if you need to, so you can attack such creatures normally."
A tiny creature (with a reach of 0') does not threaten adjacent squares, but it does threaten it's own square. Conclusion: Your own square is not adjacent to itself. Further conclusion: A creature occupying a square if not adjacent to itself.
I would absolutely house rule this if it made sense, though. (Allowing the spirit wisps to attack a creature that is sharing the square of the barbarian)
can they consider themselves a foe for a specific ability?
I don't think the rules really cover this.
I would probably generally not allow it, especially if it's cheesing out an ability like using them to heal yourself. If you're being healed by the wisps, you're generally in favor of this, so considering yourself a foe to make this happen doesn't really make any sense.
No you can not be adjacent to yourself because you can not be in two places at once.
The combat chapter generally refers to "Adjacent squares".
No you are not your own foe. By the rules you are your own ally for the purpose of most affects.
The book says enemies in within 5 feet are counted as adjacent. There is no reference to allies.
What you are basically trying to do would be called "gaming the system" so even if the RAW did allow it many GM's would say no.
If you are trying to heal undead, this will not work. It states 'living foe' right in the description. Any living thing with negative energy affinity or the like would get hit and healed, but it still has to be a living foe, not an ally.
Other than that, what Grick and wraithstrike said.
I can already see the next one: "What if I'm Large or larger and take up two squares? Am I adjacent to myself then?"
It would be fine for an NPC ability -- a decent number of undead have the ability to heal themselves endlessly. I've run at least two of them in APs. But it would be overpowered for a PC to have endless free healing (I'm betting you're looking at Dhampirs, Death domain cleric or some other ability that switches your positive / negative energy affinity).
I can already see the next one: "What if I'm Large or larger and take up two squares? Am I adjacent to myself then?"
It would be fine for an NPC ability -- a decent number of undead have the ability to heal themselves endlessly. I've run at least two of them in APs. But it would be overpowered for a PC to have endless free healing (I'm betting you're looking at Dhampirs, Death domain cleric or some other ability that switches your positive / negative energy affinity).
Bones Oracle with Resist Life and the Lame Curse. Multipurpose 1 level dip at that point if it functioned and plenty flavorful.
I'm fine with it not functioning. For the most part, I asked because I couldn't locate a good working definition of adjacent in the game rules when it didn't specifically reference squares.