The Walking Flora Save for a few lower forms of algae and fungus, that periodically revive and dry up, most plants have learned to relocate themselves in some way. The unmoving flora often produces seeds, able to fly far and stay long dormant. Plants are still plants, ie they use sunlight as a vital part of their metabolism. Typical examples, in order of evolutional appearance:
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The Eternal Road-runner is very akin to the desert plant known from so many movies. Once free from roots, it slowly travels the world, helped by the winds only. The base of its roots stay, and should some scrub come to the location again, and find good soil and water, it can re-use them. Widespread for some time, several other lifeforms have learned to use the abandoned roots to their advantage. The road runner is the forefather of many other plants.
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The Slow Walker is heavier, and much slower. It can move, pumping its intern fluids ("pumping" aided by the sun's warmth) from one part into another. While indeed slower, it is actually the first plant that can be said to _search_ for better soil, as it chooses its direction. It has primitive senses, but no intelligence to speak of. If it is getting too dry, it first reverts to the road-runner stage, and dies later.
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The Wanderer is much better at walking, and does it almost all the time. Still stoppping to root during nights, it has the habit of taking fine soil with itself, and processing it while on the road. The carrying branches start to resemble legs, and were it not for the smaller branches and leaves, it could resemble a big spider or insect (with an irregular number of legs of course). Wanderers seem to have some memory of the path they use, but it is probably based on the planet's magnetic field, so many go astray when the magnetic field goes wild. The Wanderers, grew spikes equipped with strong toxins to stay safe from the Floaters. (Note: The long-term consequence may be a turn towards a more carnivorous mode of survival...)
Fauna outside of the seasWhatever wants to survive above, needs to equipped for the Floaters. Some stay small, the rodents and insects darting or creeping between plants and holes. Some mask to look like plants, or mask themselves with plants, even growing them on their back. Still others use toxins to taste bad to the Floaters. Whatever, too obvious movement is not to their advantage.
The Floaters - "Jellies"Simply put, REALLY big sacks of methan and other light gases, floating above the lands and eating whatever the Gods don't feel a liking to.
Actually, the jellies are solar feeders, with algea impregnating their sacks... supplementing their food with other things. But even with the support of photosynthesis, they are quite hungry. A good sized one can be 500 meters across, with long tentacles groping on the ground, designed to blot out the sky and make people stop with gaping mouths (in doing so, likely sealing their fate).
The gigantic "jellies" are not intelligent, not even truly sentient, they don't need it. With powerful senses and simple instincts they can handle most threats easily, and for some time should be unquestioned masters of the air (note that "some time" may take millennia). With sight ranging not only into the infrared parts of the spectrum, and a sense for the planets magnetic field (for orientation but also against storms) they are THE beast of this world. Imagine gigantic satellites floating and scanning and eating whatever seems suspicious... while not intelligent, they may have a vast memory of the things they have seen and tasted.
Option: It is not one gigantic organism, but actually thousands of colony creatures like real world jellies. So even shooting them down wouldn't help much... all you do is spread spores around in the gigantic explosion, and make thousands more, plus all the eco havok the various pieces will generate on the ground.
Theory: One thing that Floaters would not like are storms (strong winds in general, but storms especially). If they secrete the right substances, they could influence they way water vapours condense into rain-drops, prolonging the period of rains (but weaken them), or hinder rain altogether and make the water condense as moisture. Both cases could have a positive impact on the ground flora.