xF2 Add-on Custom 404 Page by Siropu 1.2.0

This add-on allows you to customize your 404 error page, keep track of missing URLs and redirect them to new pages.

It comes with a basic error message but you can customize the page the way you want it using HTML and XF template syntax, having the option to hide the header and the footer.

Log can be found in ACP > Tools > 404 not found