World's Finest Comics #206 (On Sale: August 5, 1971), has a Superman/Batman cover by
Dick Giordano.
We begin with "The Secret of the Captive Caveman" by Bill Finger and Jim Mooney and reprinted from World's Finest Comics #138 (1963). Batman and Robin attempt to capture an alien being spotted in Gotham City. When the alien realizes his Z-Beam weapon doesn't affect humans he rushes to the Gotham Library to learn why. There Batman and Robin overhear the alien tell its superiors that their weapons cannot affect modern man. Before the two heroes can capture the alien he swallows a pill and dies and his comrades in a ship outside breach the time barrier to escape.
Seeing a history book opened to the time of pre-historic man, Batman and Robin deduce that the aliens have traveled back in time to try and conquer the human race in the past. Calling Clark Kent at the Daily Planet to tell them of this plot, Clark tells them that he will meet them in the past. Batman and Robin then use Carter Nichols' time machine to travel to the stone age in the hopes of thwarting the alien invasion of the past.
They all arrive in the past before the aliens do and after saving a tribe of cavemen from a sabretooth tiger, Batman, Robin and Superman disguise themselves as cavemen and wait for the aliens to arrive. When the aliens arrive their Z-Rays work at making the early humans their slaves. The three heroes pretend to be enslaved as well so that they can learn of the alien plot. They have the cavemen mine for a rare metal called Drakkium, an ore that -- unrefined -- is harmful to the aliens. The aliens intend to use the unrefined ore to take over the leadership of their race and then refine the ore, which ironically is deadly to humans, and use it to wipe humanity off the face of the Earth and take over the planet.
Batman, Robin, and Superman then free the cavemen and stage a revolt against the alien would-be dictatorship by incapacitating them with chunks of unrefined Drakkium The alien force unconscious, Superman, Batman and Robin then turn the insurgent force over to the alien authorities and launch the remaining unrefined Drakkium ore into space with an alien ship. With the threat over, Batman, Robin, and Superman return to the present.
Next up is "The Creature That Was Exchanged for Superman" by Jerry Coleman, Dick Sprang, and Sheldon Moldoff and reprinted from World's Finest Comics #118 (1961). While on a charity drive for the Heart Fund, Batman, Robin and Superman spot a strange energy beam outside the city and decide to go and investigate. Superman is teleported away and replaced by some strange creature. Concerned about this creature's sudden arrival, Batman and Robin attempt to rope it up, but it breaks free and begins to tunnel into the ground. Batman, spotting a boulder at the top of the hill it's boring into, comes up with an idea of how to attack the creature.
Meanwhile, Superman finds himself transported to the planet Xeron by an alien named Vathgar. Vathgar explains that he transported the creature to Earth, but one drawback to the device was that the transported creature has to swap places with something at its destination. Not wanting Superman, the aliens attack him but he is impervious to their weapons. However, when he uses his heat vision he finds that it freezes things instead of melting them, and his flying powers are wonky and Vathgar manages to get away.
Flying to a nearby city, Superman sees a runaway vehicle and attempts to stop it by using his super-breath only to find that he has flame breath instead. When the people of Xeron attack him, Superman convinces them to stop to compare notes. He learns that Vathgar is a criminal on this world and that he had captured two Skrans, and the inter-temporal transport device for some unknown purpose. Superman agrees to track down Vathgar to learn his purpose.
While back on Earth, the Skran sent there comes out of its tunnel and no matter what Batman and Robin attempt to do to stop it, some impenetrable force keeps them from stopping the creature. While back on Xeron, Superman tracks down Vathgar and learns that he sent the Skran to Earth because there is an element there that is rare on Xeron that makes the Skran invincible and he intended to use the creatures to overthrow the government and take over his world. Superman is forced to battle the Skran that Vathgar has and realizes that extreme cold renders the creature harmless when he uses his freeze vision on the creature.
Back on Earth, the military fires all their artillery at the Skarn there causing it to split in two. One of the creatures passes through the returning teleportation beam, returning Superman to Earth as well. Superman flies off and comes back with a large chunk of ice to drop on the Skarn to render it harmless. With the beast quelled, the heroes bring it off to the Gotham Zoo to resume the remainder of its docile life.
That brings us to "Riddle of the Four Planets" by Jerry Coleman and Jim Mooney and reprinted from World's Finest Comics #130 (1962). An alien starfish creature lands near Wayne Manor and Batman and Robin go to investigate the creature. An alien ship lands and the aliens explain that the creature is a Zelaphod which they accidentally unleashed. They also explain that the creature grows in strength and size and gains the ability to fire explosive bursts of energy by sapping minerals deep below the surface of a planet and is seemingly indestructible. When Superman arrives, they find that the creature proves impervious to Superman's strength and x-ray vision. The alien tells them of an old poem that itemizes ingredients to a chemical compound that can help them defeat the monster.
Telling them the title of the poem -- Sauk -- contains the first letters in the names of different planets that supposedly have the key ingredients. With this information, they alert Commissioner Gordon of the creature and fly off to the various worlds to collect the ingredients they need.
Superman travels to the planet Sinzar to find "sand from the beach of a waterless sea", and upon freeing a trapped archeologist finds exactly what the poem is talking about: a dried-out beach in front of an ancient city buried underground. On Antella, Superman seeks out "moss from a barking tree", which he finds on that worlds "forbidden forest" region after destroying hallucination inducing plants and finding that the poem verse is not quite literal: He finds the moss in a tree that is defended by a small dog-like creature.
While elsewhere in the universe Batman and Robin arrive with the traveling band of aliens to the planet Unxor. There they agree to put on an acrobatics show when the alien cast comes down with space measles. After putting on the show, the aliens gladly tell them where to find "Ears that hear the music of the morning knell" which turn out to be ear-shaped plants that are around giant singing boulders. When traveling to the planet Karos to collect a "tuft of hair from the mystic Krell" they have to battle a giant reptilian creature - a Krell. Although they are overpowered Superman arrives and lends them a helping hand by taking a tuft of hair from the creature. In the aftermath of the battle, Batman notes that a strange gem is shining energy on a hole in the ground shaped like the Zelaphod creature and deduces that it is the source that makes the creatures a threat to the universe.
Destroying the gem to prevent any more Zelaphod threats in the future, Batman, Robin, and Superman return to Earth with the mixture of items and use it to destroy the Zelaphod that is threatening Gotham City.
We end with "The Mirror Batman" by Jerry Coleman and Jim Mooney and reprinted from World's Finest Comics #121 (1961). While attempting to stop some crooks from robbing a warehouse, Batman accidentally falls into a mirror which transports him to another dimension. Robin is unable to bring Batman back, so he contacts Superman for help. Batman emerges from the mirror, altered by it and given bizarre powers.
While Superman and Robin try to corral Batman, the thieves return to steal the mirror, locking in their hide-out safe. Batman is brought down by Superman, but can only be returned to normal by returning to the mirror’s dimension. Finding the mirror missing, Superman and Robin track down the thieves and recover the mirror.
The trio then enters the mirror and meets a strange being responsible for Batman’s transformation. Superman agrees to defeat Xanu, the being's enemy in return for returning the Caped Crusader to normal. Once the task is done, the trio return home, and Superman smashes the mirror.
Edited by E. Nelson Bridwell.