How do I send my contestant a link to check their entries and their unique URL?

Format the link like this:

http://vyper.io/c/6222ggryh?email=EMAIL

Where EMAIL is your registrant's email address.

For example:

http://vyper.io/c/6222ggryh?email=tyler@vyper.io

Note:

You'll have to use your mailing list provider's option to pull in their email address dynamically in order for this to work.