You're probably looking for a quick answer such as a spell but entering into someones dream would be hard work if you believe it's possible.
First you should study and practice lucid dreaming otherwise you could forget the dream or have it out of your control. Lucid dreaming is being able to control and remember your dreams.
Once you're good enough at lucid dreaming you should start with astral projection or you and that person could meditate together. Astral projection is either making your soul leave your body or projecting your consciousness into a different place.
It all depends on your belief because there are different ways to do it for each belief that say it's possible. I recommend researching it more as well as astral projection and lucid dreaming to start you off.
Entering someone elses dreams has absolutely nothing to do with astral projection. It is known as "dream walking". People do it at times without even meaning to. I personally believe it is possible, due to the fact we are all connected on an energetic level. Even with years of practice, it is not always something you can control.
If you really wish to do this, research "dramertime". It may tske a bit of digging, but is a worthwile project. Things you can do to help with your efforts would be dream journaling, learning to sense energy shifts when someone goes to sleep, learning to recognize when you are dreaming (lucid dreaming), gaining control over your dreams, and I would suggest finding a practice buddy once you get to acutally dream walking. This can be a lengthy process.
For those whom are wanting to do this to mess with people or control them.. dream walking does not give you control over the person. It is also not the best idea to use to mess with others. Our minds do have nstural protection when in a dream state. When in someone elses dream, their subconscious is in control. To try to alter things will most likely cause them to go on defense mode and either end up with you tossed out or in a nasty nightmare. I am not accusing the poster of having such an intent, but others have joked about giving others nightmares and I figured it was worthwhile to mention. Enjoy your research!
I never denied it had nothing to do with astral projection. In fact that is exactly what I stated. Astral projection is not the same as dream walking. Nor can you enter someones dream through the astral. When you astral project you go onto the Astral plane. You may see others there, but that is not the same thing. However I do believe you could connect to someone in this manner via etheric projection, as we do not leave this plane in sleep.
You can enter into someone's dream and thoughts via telepathy and when you enter, only then you can communicate with them. I do that often for my clients because it takes a lot of practice and they have no patience.
Like said before, it's an invasion of privacy and should only be attempted if there is a REALLY good reason. Doing it for fun is wrong in many ways. Please don't tamper inside others subconscious.
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Hope this helped.
Blessed be.
