This papercraft is King Boo's Crown, the final piece of jewelry Luigi collects before he saves Mario in Luigi's Mansion, the paper model created by Seb. In Luigi's Mansion, the crown holds a red diamond at the top. Officially, King Boo's crown also counts as a Red Diamond. The crown is worth the same amount as a single coin.
The crown has changed in the later Mario games it has appeared in. It is nowadays shown as a golden crown encrusted with jewels, similar to Princess Peach's crown.
In Luigi's Mansion: Dark Moon, however, King Boo appears to sport the crown's initial appearance, except the gem, which is different and gives him enough power to shatter the Dark Moon. [Source: mariowiki]
You can download this papercraft model here: Luigi's Mansion - King Boo's Crown Free Papercraft Download