Most of the time, it should be really easy to determine who is my ally and who is not. The people who try to kill me are most likely my foes, whereas the people who entered the dungeon with me are probably my allies.
But sometimes it’s not that simple. What if one of my party members got replaced by an evil doppelganger, who plans to kill me in the near future? What if one of my allies infiltrated the court of the evil king and I accidentally have to fight her, while she is (unbeknownst to me) under the effect of a disguise self spell? What if a character fell in love with the BBEG and just wants to save him from himself, while the BBEG hates the character and actively tries to murder him?
Most spells and abilities that affect others specify the targets as “creatures” or “willing creatures”. Some explicitly affect allies only. That’s why I want to know, how to determine who’s allied with whom. Do I have to think that someone is my ally for someone to count as my ally? Does someone else have to believe to be my ally in order to count? Do both of us have to agree on being allies? Is there an objective observer who determines who’s allied? Can Person A be the ally of Person B, while Person B is not the ally of Person A?
There are many examples for spells/abilities that care about allies, among others:
- the Exalted Champion feature from the Oath of the Crown Paladin
(SCAG, p. 132-133), that grants allies within 30 feet advantage on Wisdom saving
throws. - the Inspiring Surge feature from the Purple Dragon Knight
Fighter (SCAG, p. 128), that allows one or two allies within 60 feet to make
a melee weapon attack as a reaction.
With features like this, you could accidentally affect someone who’s not actually your ally. You could fail to affect someone who is actually your ally, but you don’t know it (yet). Or you could affect someone who doesn’t want to be affected (because they don’t want to be allied with you). This all depends on the interpretation of the word “ally”. I’m not sure if "ally" is a defined game term (but I don’t think so), or if I have to rely on the dictionary definition. That’s why I want to ask:
How do I determine who’s allied with whom?
Best Answer
Ally is not a precisely-defined term in 5e D&D.
You are unfortunately dependent on the normal English meaning of the word, and thus it is largely the DM's ruling as to whether or not two creatures count as allies or not on a case by case basis. The Oxford English Dictionary defines an ally (in this sense of the word) as:
Personally, I would tend to rule that creatures are allies if they are co-operating together and would both agree that they are allies at that moment, and so abilities that affect allies do not affect creatures that you do not currently regard as allies or that do not regard you as an ally.
This does allow for alliances of convenience - two creatures who are entirely unfamiliar to each other but nonetheless find their lots thrown in together could treat each other as allies if they like. Say, for instance, two prisoners who do not know each other but are thrown into the arena together to face a beast - if they're willing to work together, they can be allies.
It also allows for deceptive alliances; say in the example of the doppelganger who has infiltrated the party. They may ultimately plan to betray the other members, but it's perfectly acceptable for them to consider them as allies and thus get the benefit of allied abilities up until the moment they turn upon them.
Making it simple
If the precise classification of who is and isn't an ally ends up taking up too much table time or prompts arguments, then as a house rule you could simplify such targeting rules by replacing references to "ally" with "willing creature you choose". There are a probably a few edge cases where this might cause a notable change in effect resolution, but it seems to me that in most circumstances it would result in targeting which was consistent with the intention of the ability.