|The constellation Monoceros was invented to fill in a big gap in the winter sky. The ancient star watchers don't seem to have been overly concerned about the sky in a cartographical sense, so they recognized Orion and Hydra and associated them with mythical stories, but they left the dim area in between as a sort of no-man's land. It's like the early maps of the United States where large areas are simply marked "Indian Nations."
A 17th century Dutch guy named Petrus Plancius decided to name the area after the unicorns mentioned in the Bible. So it's not directly associated with any of those wacky ancient mythical stories, other than the ones in the Bible.
The Rosette Nebula is a large massive cloud with lots of adorable baby stars and jealous star wannabees. It's mostly made of hydrogen and helium and a few other things that probably don't smell nearly as nice as its namesake.
Messier 50 is an open cluster of young stars still in a tight little social clique like a bunch of kids pretending that high school doesn't suck.
Open clusters are families of new stars and they are good markers of the spiral arms of our galaxy. For some reason we say they are sisters, as though stars are female. But in most traditions, the sun is male. There are rare exceptions, like the Cherokee and the Inuit, for which the sun is female and the moon is male. I guess all the celestial objects are gender non-specific so it's not important where they pee.
The Christmas Tree Cluster is a large area of nebulosity and young stars and other gaudy ornaments. It only vaguely looks like a Christmas Tree and only if you are one of those people who goes to Terror-Threat-Level-1 because the Starbucks barista wished you happy holidays.
The Cone Nebula is a column of dark dusty material which is obscuring our view of an otherwise clean example an emission nebula, unfortunate for people with unreasonable expectations of tidiness from fluorescing hydrogen excitation. But it's perfect for people who realize that without dark stuff there would be no concept of light stuff. There would just be stuff.