What happens if multiple people cast the Dream spell targeting the same person at the same time?

Question

The description of the Dream spell says, in part:

If the target is asleep, the messenger appears in the target's dreams and can converse with the target as long as it remains asleep, through the duration of the spell. The messenger can also shape the environment of the dream, creating landscapes, objects, and other images. [...]

So what happens if someone else is already in the target's dream when the spell is cast? Would the two messengers be able to converse with the target simultaneously? Would they even be aware of each other? Which one would get control of the environment?

The situation may sound absurd, but one could imagine an important person who wants his dreams to stay private might employ someone to cast Dream on him each night if it would prevent other people from doing so.

Answer 1

To quote the PHB on "stacking" spells:

Combining Magical Effects

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect-such as the highest bonus-from those castings applies while their durations overlap.

For example, if two clerics cast bless on the same target, that character gains the spell's benefit only once; he or she doesn't get to roll two bonus dice.

Basically, this means that the second casting of the Dream spell would be wasted, in RAW.

That said, I don't see why you can't have some fun with it. Looking at how the human mind works, there are rare cases where two halves of the brain can work independently of each other (I have personally experienced this, and it is weird), causing you to either interpret the same thing differently, at the same time, or even to perceive two completely separate things at the same time.

Either that, or just give them all control over the recipient's dreamscape — fighting for control. I can definitely see a group of Wizards arguing as they try to build the dreamscape around them; or more appropriately, using the target's dreamscape to set up a bar, having decided it's a fabulous meeting place since the psychological decorations are top notch and the existential angst is tuned to just the right frequency.