The drownviper attempts to strangle Kong during their fight in the lake. This is a homage to the Elasmosaurus attempting to strangle Kong during their fight in the 1933 classic.
Kong unleashes a barrage of punches on Godzilla in Egypt after knocking him down, which is a callback to their original fight on Mount Fuji in King Kong vs Godzilla.
In hollow earth, Kong fights with a serpent-like creature called the "drownviper". This could be a callback to King Kong Escapes where Kong battles with a giant sea serpent.