Let's take a look at the Sand Demon, Tokamak and Killer Frost through the pages of DC Comics!
Golden Age Flash reprint guide for more info on this!
...but there wasn't much of an explanation for the return of Tokamak....
...who so impressed Superman that the Metropolis Marvel recommended the Nuclear Man for membership in the Justice League of America, which more can be read on here!).
Pied Piper, that faced Firestorm in his Fury of Firestorm title and they've been covered in previous Flash Facts!