Badder

Comparative form of 'bad'; more bad, worse, or (in slang) more impressive and tough than something else.

From Old English 'bædel' or similar, with the regular comparative suffix '-er.' In standard grammar, 'worse' is preferred, but 'badder' persists in dialect and modern slang (especially African American Vernacular English), where it can paradoxically mean more badass/impressive.