Sigmund and the Sea Monsters (1973)

S1E6 The Nasty Nephew

Aunt Zelda invites her nephew Leroy to stay for the weekend, but he is set on being difficult with the boys. An initiation prank involving Burp and Slurp, where they blindfold Leroy, only adds to the tension. Meanwhile, Burp and Slurp take Sigmund back to their cave. When Johnny and Scott decide to sneak out and save Sigmund, Leroy tags along. Faced with the choice of revealing the boys' secret or staying loyal, Leroy must decide what to do when he finally encounters Sigmund.