Wandering Dream

This spell inserts a sleeping messenger into another creature's dreams, and is essentially a weakened version of the fifth-level Dream spell.

While the Dream spell allows full control of the target's dream, Wandering Dream only allows the caster to insert a messenger into a dream. Importantly, as this is a normal dream, albeit with the messenger inserted, the target may not remember the dream, unless other magic is applied. The messenger does remember, however, as the magic of this spell is being cast directly on them.

Choose a creature known to you as the target of this spell. The target must be on the same plane of existence as you. Creatures that don't sleep, such as elves, or creatures that do not connect to the dreamscape, such as kalashtar, cannot be contacted by this spell. A willing creature you touch falls asleep for the length of a long rest, if not already asleep, acting as a messenger in the target's dreams (replacing the messenger's own dreams), while you go into a trance, acting as a conduit between the two, thus able to view the dream from an outside perspective. If the messenger cannot fall asleep for whatever reason, the spell fails.
While in the trance, the caster is aware of his or her surroundings, but can't take actions or move. While in the dream, the messenger is instinctually aware that they are not in their own dreams. Likewise, the target may know the messenger to be foreign to their dream.
While this spell cannot target creatures disconnected from the dreamscape but still able to sleep, such as kalashtar, it can still use them as a messenger in a target's dreams. Sleepless creatures, such as elves, cannot be used as messengers. Anyone with the ability to do so can cast the spell.

If the target is asleep, the messenger appears in the target's dreams and can converse with the target as long as both it and the messenger remain asleep, and the caster stays in their trance state. The caster can end their trance at any time, severing the connection. The caster has minor control over the environment of the dream; being able to create small objects and such at the user's request, but changing larger parts, such as the landscape or nature of the dream (which is possible with the standard Dream spell), is out of the question. The messenger cannot shape the dream, only interact with it and the target through it, as it is not theirs.
If the target is not asleep, the caster knows it, and can either end the trance (and the spell) or wait for the target to fall asleep, at which point the messenger appears in the target's dreams. Until then, the messenger dreams normally.

How the messenger appears in the target's dream is mostly determined by how the target sees the messenger, and the nature of the dream; but, slightly influenced by how the messenger sees themself. How the messenger sees themself is also used as a fall-back in case the target does not know the messenger, but this perception is still influenced by the dream. The nature of the dream can change due to external influences such as the Dream spell, which will change how the messenger appears along with it.
This often means that the messenger could appear as anything, ranging from a great hero, to a literal rat, to just themselves in different clothes.
Despite changing appearance, the messenger still retains their mental faculties; it is the one thing separating them from the dream. (Your Intelligence, Wisdom and Charisma stay the same, even if your form changes.)
If the target's perception of the messenger allows it, you can make the messenger appear monstrous and terrifying to the target. If you do, the messenger can then deliver a message of no more than ten words, and then the target must make a Wisdom saving throw. On a failed save, this starts a nightmare influenced by the messenger's appearance and words that lasts for the duration of the target's sleep, and prevents the target from gaining any benefit from that rest.
Either way, the spell then ends if used like this, and cannot be used again with the same target for the duration of the target's sleep.

If either the target or messenger wake up, or the caster ends their trance, the spell ends, and the messenger returns to their own dreams. The spell does not magically extend sleep, only initiate it in the messenger.

If the messenger no longer wants to be in the dream, they can either try to find an escape within the dream, or wake up the target. The messenger is otherwise unable to wake up willingly.