The whole question goes like this:

What magical abilities such animals could develop or magically enhance existing ones to greatly increase the likelihood of drastically outliving an average specimen

Some clarifications

  • An indeterminately-growing animal is, well, an animal that never stops growing
  • The animals I'm mostly interested in are snakes, lizards, amphibians and fish (mainly sharks) as well as crustaceans (if that helps)
  • Most animals (the exception are the magical species) in my world start manifesting magical abilities with clearly visible effects after approximately 100 years in areas with mundane magical activity (also varies with size and intelligence, with small and intelligent being the fastest to achieve it)
  • Since the abilities develop during life, and are a subject to environment and thus diverge between individual specimens, but still share visible common elements across the whole species (think bending in ATLA)
  • The only factor i can think of that my magic system would not support in almost any form of rapid transformation (shapeshifting etc.), otherwise anything goes, demons, ghosts, gods, undead, eldritch horrors and the like


A serpent developed a connection with a dark deity while living near its temple, and now said deity recognizes the serpent as a pet/living weapon, and with it's followers cares for it.

A species of giant swamp toads has a tendency to "learn" how to bend light around itself to camouflage for hunting and create mirages to confuse predators, which can evolve into the ability to affect not only light, but also empty space for short periods, improving hunting and evading abilities.

  • 1
    $\begingroup$ Do you want them to only live longer or have a way to deal with size problems(square cube law) and energy requirements issues as well? First is relatively easy and might not even need magic(except for giving them the natural qualities without evolution), second is going to require some magical kajiggering $\endgroup$
    – Rubrikon
    Dec 19, 2021 at 22:33
  • $\begingroup$ @Rubrikon the first one (I feel like magic needs to be here, cuz I wanted to have some beasts that are hundreds of years old), but I wouldn't say no if you have some ideas for the second one :b $\endgroup$
    – acki02
    Dec 19, 2021 at 22:41

3 Answers 3


There's essentially two components to what the magic needs to accomplish here:

Biological changes to make the animal immune to disease and cancer and allow growth beyond what the species evolved for while still remaining functional.

Secondly the magic needs to prevent deaths from predation or starvation. However the second goal is pretty much trivial, since an animal with bending is laughably OP compared to one without.

If you're not attached to every affected species getting immortality, then you can include the bending part and let evolution do the rest: Since bending would select for a long lifespan, because it can eliminate normal metabolic constraints and allow for a creature to have many times as many offspring.

Thus bending would naturally push affected species towards taking advantage of it: Until eventually many species will only reach sexual maturity after 100 years. At which point some simple organisms like tube worms might evolve to switch to focusing entirely on reproduction and begin generating their metabolic energy directly through bending.

Every bending ability described is quite powerful, but what animals learn is unpredictable. So in animals that can't gamble on a miniscule fraction of their offspring surviving there will be a strong selection for intelligence.

I expect staying dormant for most of the first century of life to become extremely common. Moreover I anticipate some species simply evolving eggs that can stay viable for a century because of the huge advantage that would provide.

  • $\begingroup$ The problem is, while the base for the magical abilities is genetical, the abilities itself aren't. From the same brood of kittens you could get a lion with a wind-based leap-boosting ability, and one that has a hallucinogenic mental attack, just because those two lions learned different things. $\endgroup$
    – acki02
    Jan 5, 2022 at 19:54
  • $\begingroup$ @acki02 Even if there's no way to consistently get specific abilities, animals like tube worms have millions or billions of offspring. So they can afford to gamble on only a miniscule fraction learning the right magic to survive $\endgroup$ Jan 5, 2022 at 22:30
  • $\begingroup$ would it "help" if the reproductive capability were to "burn out" by the magic? Also (as I mentioned) that magic is heavily (although forgot that part) tied to amount of neurons, so things like plants or jellyfish have absurdly low chances of having serious magic $\endgroup$
    – acki02
    Jan 5, 2022 at 22:39
  • $\begingroup$ Ok yes this is important information you should have included in the question because it makes a big difference: $\endgroup$ Jan 5, 2022 at 22:41

Overcome the Square-Cube Law

The square cube law is basically the thing that says that as an object grows in 3 dimensions, the toughness of any part of it is determined by a 2-dimentional cross-section.

The biggest danger of indeterminate growth is that you will quickly become so big that you can no longer support your own weight and some very important part of you crushes ending your life; however, the are ways to ignore the Square-Cube Law.

One way is to scale up so that height scales much slower than length or width. Your snake body plan for example can get much longer, and only a little bit taller. So by the time any part of the snake is tall enough to get the cross-sectional weight of a normal large animal, it could be a hundred of meters long.

Another option is an environment that supports the whole body. Water for example allows for very large animals like whales to exist in neutral buoyancy. Some species of whale can grow to a mass of about 200 tons just fine. Another similar option could be living underground so that all of your parts are supported locally like the roots of a tree: so you could picture perhaps some sort of giant underground squid or jellyfish that covers a large area and has tentacles that protrude just to the surface to act like a bunch of sperate ambush hunters, or perhaps it is a herbivore that grazes on all the vegetation that grows above it.

Beyond the square cube law, the second biggest obstacles will be food and circulation. Many body plans have 1 mouth and 1 respiration point which can lead to very long and inefficient systems in megafauna. So a creature that grows multiple local digestive and respiratory systems may be able to get bigger providing it can find a food source to meet its feed to its many mouths.

So... basically, your biggest of the big mega fauna will end up resembling some sort of Lovecraftian horror.

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To balance out the long lifespans, you would essentially need your animals to have long hibernation periods. You could build a world where as the animal grows, the need for food decreases or that the need to feed regularly disappears. Now since the environment is already saturated with magic, I expect the animals to absorb some of it. If they absorb enough, the magic can help regenerate dead cells at a much faster rate. If this continues for long enough, perhaps the animal becomes essentially invincible (e.g., the moment a sword piercing this snake is removed, it heals from the wound). For particularly old animals (30,000 years) you could replace their biological need to eat with absorption of magic in the environment.

Another thing that you can do is stop the physical growth. In normal world, animals grow up to a certain size till a certain age and stop growing so much once they reach adulthood. It could be the same there. You could remove the reproductive system after a certain age, even replace hearts with pure magical cores.

The skill an animal is learning would also probably depend on their upbringing and inherent abilities. For example, a lame lion would learn speed or stealth while a lion who has generally starved throughout childhood would learn to be a better tracker. For smaller animals you could try increasing their size just enough that its natural predators would be afraid of it.

Lastly, you could make the animals less violent than their normal counterparts. They will generally not pick fights with smaller animals if there is no need. I believe an animal smart enough to learn magic will be smart enough to maintain truce with other animals like itself, i.e., with magical abilities because it will simply not take the meaningless risk just for thrill or food, if it doesn't need it. If you do, however want to make your animals violent, I suggest a specific reason. For instance, if animal A defeats animal B in combat and kills it, A will gain the magical abilities originally belonging to B.


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