Bat-Mite and Thunderbolt, Metamorpho and Plastic Man. These were two sets of counterparts on Earths One and Two capable of manipulating matter, often their very bodies, into various shapes and form in their haphazard crusaders for justice.
That said, when Plastic Man migrated from his native Earth-Two ultimately to Earth-One, this meant two of "him", and in fact he later faced his counterpart Metamorpho once in battle. How would the cosmos reconcile this inequity? Simple. Bat-Mite around the same time period left Earth-One for Earth-Prime in an attempt the gain more notoriety using the production staff at DC Comics. After this caper, he disappeared never returning to his native dimension.
However, Mite's twin on Earth-Two the Thunderbolt remained in that universe. Sure, he occasionally journeyed to Earth-One, but mostly remained on his adopted home world. Occasionally, he would duplicate himself using clones from his native dimension. As such, these Thunderbolts counterbalanced Plastic Man and Metamorpho on Earths Two and One respectively. Meanwhile, Bat-Mite's move to Earth-Prime compensated for its hero Ultraa leaving Earth-Prime for Earth-One.
While Bat-Mite's career was a scant dozen or so tales, Thunderbolts was scores of adventure. Similarly, while Plastic Man only had a couple dozen cases on his world before leaving, Metamorpho had a long and unique career both a a solo hero and member of the Outsiders.
Additionally,Thunderbolt's presence in Earth-Two's dimensional plane doubled that of Bat-Mite's. This also made up for the loss of this pliable protector, as Thunderbolt could mimic the abilities of Plastic Man and Metamorpho, and filled in the role of honorary Justice Socialite as had the latter with the Justice League.
As for the rest Thunderbolt's race, they mirror the Water Sprites whom Earth-One's Aquaman and Aqualad met a hand ful of times. Shocko, son of the original Thunderbolt, was joined by several of his peers on a view occasions assisting or annoying Earth-Two's Johnny Thunder.
Both Bat-Mite and Thunderbolt were powerful aliens that aided Batman and Robin, while Metamorpho and Plastic Man were valuable allies the Caped Crusader enlisted on occasion.