The first two issues #1 (July-August, 1972, with cover by Murphy Anderson) and #2 (September-October, 1972, with cover by Nick Cardy will be covered now!
Signalman Of Crime
Signalman would return a few times, then got a revival in the 1970s, being in the feature in an issue of Detective Comics that featured the Calculator, and being a member of the Secret Society of Super-Villains that faced the JLA/JSA.
The Crimes Of The Clock King
Clock King appeared next working with the next villain and a few others in an issue of Justice League of America (reprinted in giant size) as a Green Arrow villain, and then got a name for his alter ego (William Tockman) and motivation in an issue of World's Finest, then appeared in Crisis On Infinite Earths where he made enough connections to join the Injustice League during Invasion! along with Major Disaster and Multi-Man!
Menace Of The Giant Puppet
Puppet-Master returns with Captain Cold and others working for Doctor Destiny, then returns as the Puppeteer (a name hinted at in the original appearance) to face the Teen Titans (including Cyborg, Raven and Starfire) for H.I.V.E. (and gets an alter ego, that of Jordan Weir).
Knights Of Knavery
Joker's origin was reprinted as well in a Limited Collectors' Edition, while it took a while to get an origin for the Penguin (a story for a later time).
The Trickster Strikes Back
Trickster's first appearance was first reprinted in a Flash Giant, and the Trickster would return again and again to vex the Flash (including two Flashes in his next appearance), as well as later facing Black Lightning and Blue Devil, as well as joining the Secret Society of Super-Villains.
DC Specials that led to this issue!