Riddler's Frogmen were henchmen who worked for The Riddler.
During Batman and Robin's assault on the Riddler's Headquarters, Claw Island, Two-Face managed to destroy the Batboat that was piloted by Robin by setting off one of the Riddler's underwater mines, although Robin had escaped death by ejecting himself from the Batboat just mere seconds before its destruction. Robin then attempted to swim towards Claw Island when he was attacked and overpowered by Riddler's Frogmen, who removed his underwater breathing device and tried to drown him. Batman, whose Batwing was blasted and destroyed by the Riddler himself, saved Robin by trapping the Riddler's Frogmen in a net and tied them to a buoy. They were arrested offscreen.
It is presumed that Two Face's Thugs were Riddler's Frogmen but it was never confirmed.