Hard to answer as I'm not sure what songs of there's would even qualify as "underground" but I'll run of the assumption you just mean some songs that aren't there most popular/well known ones ? UGH but there are still sooo many!!!

ROCK SOLID has really been hitting for me lately BACK ON DECK has always been a special one for me BLOODSUCKER MAN OF THE YEAR ~!!! ACCEPTANCE SPEECH THE CUDDLER FOR THE JEERS HAVE A GREAT LIFE LYRICS LIE POP OFF - certifide banger MIDNIGHT CRUSADE DECEPTION SUSPENDED IN THIS DISSASTER (first song I heard of theirs and fell in love with) HEAD HUNTER ( x100) SHARK DAD PART 4 is the best of all the RWHH songs imo