Bill Erickson

Gary Jones

Customizing the contents of the Page Not Found page in any WordPress theme can be tricky, and usually involes editing the 404.php template file. The Genesis Framework already abstracts the default content of the page into a function, and this plugin can unhook that and replace it with your own custom title and content.
Use [genesis-404-search] shortcode to add a search form to the page.
If you’d like to dynamically list content (ex: most recent posts), I recommend you install the <a href="https://www.wordpress.org/extend/plugins/display-posts-shortcode/" rel="nofollow ugc">Display Posts Shortcode</a> and use it in the 404 page’s content.

Genesis 404 Page

Customize the content of the 404 Page within the Genesis Framework.

Ron Rennick

marksabbath

StudioPress

Nathan Rice

seothemes

This plugin allows you to assign WordPress navigation menus to the secondary navigation menu within the Genesis Theme Framework on a per post, per page, or per tag/category archive basis. The per post, page, category or tag setting overrides whatever menu setting you have in your Genesis Theme setting. It does require that you have your Secondary Navigation enabled in your Genesis Theme Settings.
<a href="https://ronandandrea.com/" rel="nofollow ugc">The Author</a>
<a href="https://www.studiopress.com/plugins/genesis-simple-menus" rel="nofollow ugc">Plugin Page</a>

Genesis Simple Menus

With Genesis, Simple Menus allows you to select a WP menu for secondary navigation on posts, pages, categories, tags or custom taxonomies.

Genesis 404 Page vs Genesis Simple Menus