The Circle of the Shepherd druid's Spirit Totem feature can summon a spirit that grants certain benefits. One of the options it can summon is the Bear Spirit (XGtE, p. 23; emphasis mine):
The bear spirit grants you and your allies its might and endurance. Each creature of your choice in the aura when the spirit appears gains temporary hit points equal to 5 + your druid level. In addition, you and your allies gain advantage on Strength checks and Strength saving throws while in the aura.
In my opinion, this ability says that at the time you summon this spirit, the druid chooses creatures within the aura to get temporary HP - and only at that moment is it possible to get this temporary HP.
But I've seen people playing as if the totem provides a static ongoing effect, so whenever a new "ally" enters the aura, they get temporary HP – which made me wonder whether I've misunderstood something.
And this "static effect" approach raises so many extra questions:
If an ally can enter the aura to get temporary HP after it's placed, why can't some allies leave and reenter the aura to refresh their temp HP?
And when do those temp HP appear/refresh?
- Upon entering the aura?
- On the druid's turn for characters who are still in the aura?
Does the druid have to choose everyone who can enter the aura to gain a dose of temporary HP at the moment this feature is used? Or does it grant temp HP to anyone entering (in case of creatures summoned after the aura is created, for example)?
In summary: How does the temporary HP from the Shepherd druid's Bear Spirit work? When/how does the druid choose who gets this temp HP, and when do they get it?