This Ritual Crown plays a central role in a prophecy from Maru involving Bean, and the ultimate plan of Queen Dagmar to unlock the magic of Dreamland.
The crown is made of grey metal. Instead of just being put on the head of the wearer, it has to be screwed tight on their head. At some point before the start of the series, Dagmar, Cloyd and Becky screwed the crown onto Jerry's head, which resulted in severe brain damage that permanently rendered him mentally a child.
The crown is first seen in "The Disenchantress", when Bean discovers Dagmar's plan. She manages to escape from the Maru royal palace before Dagmar can screw the crown onto her head.
Throughout the series, Dagmar keeps plotting to get Bean to wear the crown somehow. Eventually, after Bean's evil side splits form her as Bad Bean, Dagmar intends to have her wear the crown, and unlike regular Bean Bad Bean is willing to go along with the plan. It never gets this far however as Bean kills Bad Bean. Ultimately, in "Goodbye Bean", Dagmar screws the crown onto her own head after first removing her brain, having learned from the Trøg that this is the secret to complete immortality. Because she removed her brain, there is nothing to be damaged and the crown does not impact Dagmar's mental abilities in any way.
Dagmar is still wearing the crown after Satan locks her into a cage on a cliffside with Freckles for all eternity.