What is a dream invocation
We have already learned about invocation, so let's talk about one specific branch of this practice, the dream invocation.
Dream invocation is a bit misleading term because this practice is more similar to evocations than invocations, except the evoked entity is commanded to appear in your dream, it is invoked into the dream but there appears external to your "dream body".
Some entities are supposed to give us some information or knowledge. This means we are somehow expected to actually communicate with entities, to exchange information with them. This can be done either through higher senses (clairvoyance, clairaudience, etc) or through tools (mirror, pendulum, ouija board, tarot...).
Tools like tarot are too general for the exchange of specific information, pendulum is a bit one-sided and ouija is not suitable for longer communication (plus most of us need at least one another person for ouija to work).
Black mirror is not a bad tool, it helps greatly during evocations and evoked entities can also partially communicate with us using images with symbology, but that's still not sufficient enough to replace actual talk. So, unless you have greatly developed higher senses, you will have to work with visions and dreams.
During evocation you command the summoned spirit to appear in your dream in a human form able of speech, you also should demand that you will remember the dream afterwards, you can actually use pendulum or other tool to communicate conditions of the dream. This way you can e.g. find out that the entity will appear in your dream, but you won't remember it (which sadly is sometimes the spirit's condition to appear during your sleep).
People usually think that forgetting the conversation renders the ritual useless, but the subconsciousness is a strong tool. Even if you don't remember the actual event, you can still feel assurance and relief (or opposites) based on the information you gained. That's especially useful in desperate situations.
Dangers of dream invocation
People also often ask me about security issues. Dream invocation has the same dangers as astral projection, if you allow something to happen, it will happen, so if you are seriously worried about your life, rather avoid this procedure. It's not like the worry about instant death can cause instant death, that would be a very rare case. Most of the times when a dream invocation goes wrong you will just wake up tired in the morning with a very shady recollection of what happened.
Spirit possession is about the same risk as the death, very very rare and only if you allow it. Generally a strong will with no doubts is a very important tool of Magick, this whole curriculum is based around it. If you got this far (and didn't cheat), dream invocation should be no danger to you. Your dream is yours only and nothing in your dream can go against your Will.