A striking parallel between the two primary Earths is a foes of the Masked Manhunters known as the Clock. While on Earth-One he was Batman's first foe, on Earth-Two he was Robin's arch-foe (or at least competed with Crazy Quilt for the designation).
Earth-One's Kyle initially defeated a rookie Batman years ago before the new crimefighter quickly turned the tides on the crook. Slugsy Kyle returned years later in a new costumed identity as the Clock. Using timed bombs and precision in his attacks, he now faced the Dark Knight alongside his sidekick Robin. Kyle's counterpart on Earth-Two never assumed the alias of the Clock, although a Clock would face his world's Robin.
As for the counterpart of the Clock who repeatedly battled Earth-Two 's Robin, that would be the one-shot character known as the Clockmaster. A rotund strategist like the Boy Wonder's arch-enemy, he found that the Dynamic Duo was too much for him to handle.
Then there was William Tockman aka the Clock King. Tockman was a man given a diagnosis of having six months to live. Seeking to steal from a bank to insure his infirm sister would be well taken care of, he was captured by Green Arrow and Speedy, only later finding out the diagnosis was wrong. However, when his sister eventually passed away while he was spending time behind bars, his new motivation became vengeance. He would seek Arrow out three more times while his counterpart, the first criminal Clock of Earth-Two was actually a recurrent adversary of Green Arrow's fellow More Fun Comic crusader in Doctor Fate. In the end, one conclusion remained of all these crooked cuckoos, the Clocks were history!