by JoshuaPack on WordPress.org
This plugin will simply allow you to point to a page to serve up if you get a 404 error. Also it marks it as 404.

Under Settings > 404 Settings. Add a URL to show as your 404 page. If blank, you can edit the HTML page and serve that as your 404 page.
Why choose this plugin?
This plugin does it!
This a rebel plugin that does not use WordPress’s 404 hook. It was developed for themes or plugins that cause issues with the hook itself.
For more information see FAQ page.