WWW::Mechanize is a subclass of LWP::UserAgent, so more or less anything you can do with LWP::UA you can do with WWW::Mechanize. Mechanize is just easier to use when automating click-trails (start at link such-and-such, click link named "bla bla", fill in form field "thingy", submit - etc)

The *::Mechanize::* modules linked in my post above mimic and extend WWW::Mechanize's behaviour but are probably not 100% API compatible - YMMV.