Dream and Nightmare were born in the same tree. The two are brothers and enemies at the same time, Nightmare is an embodiment of negativity while Dream is an embodiment of positivity. Dream is more protective and heroic wanting to perceive justice, Nightmare is more scornful and a villain wanting to cause destruction. They may be twin brothers, but they are completely opposite from one another but they also have similarities that brothers often have. Two are chaotic, many opposite things.