The fantasy civilization in question was stolen from this other question:
It is a civilization with Roman/Medieval/Renaissance technology, perhaps like Song or Ming Dynasty China with primitive coal-based factories. They have magical powers though. Their technology and architecture has been augmented with magical powers, enabling them to create building projects approaching those of the early 21st century in scale (for example Three Gorges Dam).
These magical powers include:
Elemental Bending: As in Avatar The Last Airbender, they are able to bend air, water, earth, fire, and their derivatives such as lighting, metal, lava, and ice. Benders are only about a 25% of the overall human population, as bending is a hereditary trait, based on certain genes, but is otherwise equally spread in almost all human races.
Telepaths can control plants and animals, making animals go somewhere for example, attack people, or cause predators to not eat prey.
Magnetic field manipulator can increase or decrease local magnetic fields.
Teleporters: able to teleport across the Universe. Some are also able to open portals and leave them open, allowing people and animals to cross between worlds without a teleporter physically present. These portals, functioning like stargates, are able to stay open indefinitely, even after the death of the original creator of the portal, until they are manually closed by yet another magic user. Portals are aimed via astrology, and can be opened onto any planet that is visible from the surface of another planet.
Astral Projection: enables the mage's spirit to exit the body, and explore the universe, outer space and other planets, without the confines of a body (No spaceship and no spacesuit needed), via the power of instantaneous teleportation to any place that the mage can visualize clearly enough. Two mages astral projecting can meet each other's spirits and communicate information, bypassing the speed of light.
Healing Magic: enables regeneration of entire limbs or organs.
They also have crystals, which enable to amplify the magical power of a user multiple-fold.
Then they also have "gods". The gods are extremely powerful magic users (capable of destroying cities in minutes and entire continents in a matter of days). Basically they are Saiyans from the Dragon Ball Z.
This civilization is "humans", although "human" here is a broader term, including more races of humans who evolved because they live on different planets. There are elves gracile, long-lived humans with long, pointy ears, more evolved brains than other humans, giving them a calm monk-like quality, less prone to logical fallacies and insanity. People with hair and irises in naturally bright colors (blue, cyan, pink, purple, and white), looking like anime characters, also having somewhat bigger eyes than Earth humans. Some people who have cat-like ears at the tops of their heads, rather than at the sides. Saiyans, near-indestructible humans, having monkey-like tails and other anatomical peculiarities, extremely powerful magic users, the "god" caste of this civilization, a very small percentage of the population, but functioning as mythological heroes, rulers, and mages, usually being the first ones to come through a portal.
This "human" multi-racial civilization are non-racist, but otherwise have the mentality of Medieval countries, having kings, knights, wizards, etc. They more or less get the gist of germ theory, wearing masks similar to those of plague doctors, having detailed knowledge of anatomy, extremely potent herbal-based medicines, disinfectants such as alcohol, iodine, and H2O2, acupuncture, and magic-based healing techniques, thus limiting the spread of interplanetary diseases. Their medicine is like Traditional Chinese Medicine, based on all natural ingredients, but they have access to millions of species from different planets to derive ingredients from. Their architecture looks like castles, pagodas, and ziggurats, but with magical improvements. This civilization is spread out among 50 or so planets, very decentralized, with each planet having one or several de-facto independent countries. Their governments are monarchies, mageocracies (ruled by powerful magic user), or dictatorships. All the planets of "human" civilization answer only to the Emperor of Mankind, who is the most powerful "god", an incredibly long-lived magic user, whose magical power is able to destroy cities and continents. The Emperor and the Prime Minister determine the overall course of human civilization, such as keeping peace among the planets and individual countries inside each planet, opening portals to other planets and colonizing those planets, planning megaprojects that use the resources of more than one planet, defending human civilization from outside threats (such as the one time when monsters and demons [hideous aliens] streamed in from the portal opened on planet Zarmon, necessitating intervention in defeating the demons and closing the portal), and protecting the native sentient and non-sentient beings of colonized planets, and preventing any forms of racism or hereditary, non-penal slavery. Otherwise the countries of the planets are completely self-governing.
They have invented a low-tech way of opening stargates to other planets. These are huge triangular arches made of pure silver, using teleportation magic together with astrology to determine the destination of the portal. Mages use astral projection to check out the planet, deeming it fit for opening a portal or is it a barren world. Once they have opened the portal, as long as the triangular silver arch is intact, the portal will be open indefinitely, allowing people and wheeled vehicles pulled by animals to casually stroll in, without experiencing anything uncharacteristic other than the sudden change in gravity/temperature/light when they step through the other side of the portal. Occasionally, a mistake is made, and a portal is opened to a hell planet, venting noxious gases out of the portal, or sucking whirlwinds of air into the portal, or freezing/boiling everything around the portal, or demons/monsters/swarming insects spewing out of the portal, necessitating the mages to close the portal at once. Because once they are opened, these portals go both ways.
This "human" civilization, magical but low tech, has colonized multiple planets, creating unique nations, cultures, and sub-species of humans, for example the planet of Avatar (ATLA), the planet of Naruto, the planet of Game of Thrones, the planet of Barsoom (John Carter). And they have also found sentient native species of those planets, integrating them into their civilization, such as the bird-men and the lizard-men, and others. So in cities where the portals are located, one can find exotic races of humans, and non-human beings wandering the streets and taverns, and exotic animals and plants being sold in the markets. The Imperial center controls the portals and all traffic going between the portals, allowing trade to be between the planets, allowing native beings to settle on other planets as well, allowing animals and plants to be resettled between different planets. So this civilization has lots of different foods to choose from. And the Imperial zoo has animals and plants from every single planet, some exotic ones with bioluminescent properties, or magical properties, or those adapted to extreme environments.
The Main Question
' The "human" civilization has several Mars-like planets in it's possession. These planets have very thin air, very cold temperature, and are deserts, having no lifeforms or few lifeforms of primitive lichens and insects. By their current state, these planets are uninhabitable to humans, and the multitude of beings, animals, and plants that they can settle into them. However the people of this civilization are very clever. They have access to countless species of animals and plants from other planets, some of which have special properties. They have magical powers listed above. They also have knowledge of planet science, such as theories of terraforming and climate change.
How can this civilization use any of the resources at their hands to terraform these Mars-like planets, to make them habitable enough to support Earth-like life? They have elemental bending, telepaths who can control animals and plants to herd them through the portals, magical plants and animals that can live in extreme environments. The end result is that the terraformed planet should allow people to live on the surface, without using airbending techniques to manually hold an atmosphere bubble around them at all times.
What are some strategies that they can use, having such resources at their hands? If there are specific magic powers, or plants/animals that you can imagine, please suggest, I can add them to the story.