The spell etherealness allows you (the caster) to travel to the Ethereal Plane for the duration of the spell (8 hours). It has a range of Self, so you cannot target someone else if cast at its base level (7th level).
However, if you upcast it with an 8th level spell slot, it says (PHB, p. 238):
At Higher Levels. When you cast this spell using a spell slot of 8th level or higher, you can target up to three willing creatures (including you) for each slot level above 7th. The creatures must be within 10 feet of you when you cast the spell.
Where it says “including you”, does this mean that:
- you can only target two other creatures, because one of these three creatures must be you, or
- you can target three other creatures, but you’re going with them (i.e. you can’t just dump these three creatures on the Ethereal Plane whilst you remain on the plane you were all on moment ago)?
Since I’m a cleric in a party of 4, I want to know if I can bring the entire party (me plus my 3 allies) into the Ethereal Plane or whether one of my allies has to be left behind…