User can become the nightmare of a target.

Pros:
-user can ward off unwanted visitors
-user's form is masked by nightmare
-user can emit sounds of the nightmare
-user  can relieve others of nightmares
-user form multiple at once

Cons:
-user will experience nightmare it is repeatedly used
-user will struggle to talk normally
-user will not physically be nightmare
-user will gain nightmares they relieve from others

Weakness: good dreams
User will become weaker and have less power when there is less nightmares.