404 page examples you need to see before writing your own.
Documention
10 examples of custom 404 pages ranked from best to worst
8 Easy Steps to Fix a 404 Error - Blog
How To Design an Effective 404 Page for Websites
Http Error 404: It's Not Always Bad! - DAGMAR
Error 404 Page With Green Numbers Vector Illustration On Black
How to edit the 404 Not Found template
An Analysis of 24 Creative 404 Error Pages - UX Design World