The attribute to set icon of this control in the Visual Studio toolbox:

ToolboxBitmap(typeof(ClassNameOfControl), "Control.bmp")

The class description is here.

You can apply a ToolboxBitmapAttribute to a control so that containers, such as Microsoft Visual Studio Form Designer, can retrieve an icon that represents the control. The bitmap for the icon can be in a file by itself or embedded in the assembly that contains the control. The size of the bitmap that you embed in the control's assembly (or store in a separate file) should be 16 by 16. The GetImage method of a ToolboxBitmapAttribute object can return the small 16 by 16 image or a large 32 by 32 image that it creates by scaling the small image.

The attribute that control showing this control in toolbox or not is ToolboxItemAttribute.

The DescriptionAttribute can be used with classes, properties and methods.

The DefaultPropertyAttribute set the default attribute of this control, and DefaultEventAttribute set the default event of this control, those will be effective when double-clicking in the VS Form designer.