Custom 404 error page

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Saurabh Rawat: My 404 page was redirect to home page but I have removed it cause of Google guideline, now I create a custom 404 error page and now my bounce rate has reached from 4% to 63%
  How is it possible (Traffic remain same)?
  My 404 page is same as home page. (Design & Content both)
  Note: I have 20,000+ "404 error pages"
• 
  Dane Morgan: You need to address your 404 errors. Simply adding a 404 page isn't a fix for having that many 404s. Even with a 404 page, they are still visitors who clicked on a link that promised them something and when they get there, the don't find it.
  
  What do you do when you don't find it? You leave.
  
  Before you were masking the problem because your home page tricked them into thinking they might have found what they were looking for and they maybe clicked on another link instead of the back button, but that still isn't a real solution.
  
  You need to figure out what people are looking for at those 404's links and put that information at that location for them.
• 
  Saurabh Rawat: I know this but my point is my 404 error page is same as home page..
  and my 404 ; page was redirect to home page before 1 month but now my 404 page is same as home page so why my bounce rate become from 4% to 63%.
• 
  Federico Sasso: 4% bounce rate is not a good value, it's just a screwed value. It probably meant your Analytics tracking code was duplicated. 63% seems a much more veritable one.
• 
  Dan B.: Sounds like somebody needs to manage their 404's better. Why so many 404's? Did you just re-architect your site? If so, you need to 301 redirect those predictable 404's to the equivalent page on the rebuilt site.
• 
  Dane Morgan: The difference is likely a problem in the way your redirection was happening. It was a false number. Unless you're site is the visual equivalent crack cocaine, you did not have a 4% to begin with.
  
  But really, your biggest most pressing concern is getting those 404s directed appropriately. Until you do that, anything else you do is just spinning gold into straw.
• 
  Saurabh Rawat: +Federico Sasso I am using Spam Filter (Hostname & Campaign Source filter both)
  
  And all 20,000 not found pages are not ranked much. Traffic is still same...
  
  I am working on 301 redirection....
  Thank you seo folks for your suggestions.