THE BEACH GIRLS AND THE MONSTER (1965)

 A goofy ass CREATURE FROM THE BLACK LAGOON-rip-off monster kills kids on the beach by scratching their faces, kids surf and frolic, a lion puppet sings a song called "Monster In The Surf"(the TV version of this was retitled MONSTER FROM THE SURF) and you get a SCOOBY-DOO ending where the shitty-looking monster suit is given a semi-explanation.  This movie feels like a 50's monster flick with a dash of Frankie & Annette BEACH PARTY thrown in along with a subplot about a cheating wife and an overbearing dad.  It's all really as dumb you would expect but worth a look if you dig extra cheesy monster thrills.  AKA SURF TERROR  For a similar but better beach/monster mash-up check out THE HORROR OF PARTY BEACH.