Overkill Central

[Lord Bookwyrm he/him]

So I'm thinking of making a monster/creature that can basically destroy cities and stuff, but it has to be something that could actually exist. For example, chasmfiends would be allowed, but a dragon wouldn't. Koloss wouldn't be allowed, but koloss-blooded might. It cannot use magic of any kind. So far, I've thought of a huge beast, omnivorous. It has scales made of organic iron and aluminium, as it swallows huge rocks to help grind the stuff it eats. The metals make their way into the scales and bones, making them extremely hard. When it sheds it's scales, it eats them to keep the metal in the system. Over decades, it eventually becomes like armour, making it hard to get through to the flesh. It has huge legs with very sharp claws (that comes as a given). It has heightened intelligence with an incredible memory. It has ten legs, each as thick as an old oak and twice as tall. It can spray acid from it's mouth and has four rows of teeth, which contain metal due to it's dietary habits. Please add anything on that you think would make it better, or make a beast of your own!

[king of nowhere]

the problem with that is the square/cube law. if you double the size of anything, its surface increases fourfold, while its mass increases eightfold. This affects particularly a creature's strenght, since it is proportional to the section of the muscles, i.e. its surface, i.e. it increases less than its mass. So basically the bigger a creature is, the weaker it is compared to its weight. That's why insects have tiny tiny legs and can carry around one hundred times their weight, humans can carry another human on their back but they find it tiring, and elephants can't carry other elephants. the bigger animals, whales, only live in water because on the ground they would not be strong enough to move.  The bigger land animals were around ten times bigger than elephants, and that's pretty much the limit; they are theorized to have lived in lagoons or lakes, where water would help them support some weight. So, make it too big and it can't realistically move.

Even if you stop at a realistic size, the creature would still be horribly slow. Elephants, rhinos, hippos can't run very fast. According to studies on bone structure and muscle mass, t-rex couldn't really run, at most trot. its prey, though, was even slower.

So your big creature, especially when weighted down by all its armor (and metal is much heavier than organic matter), would at most be able to walk slowly, and therefore it would not be able to chase anyone or anything. It would have then to rely only on eating vegetables, that cannot run away. More or less like elephants do. And elephants already spend most of their time eating to support their mass. So your big creature would eschew cities and instead roam forests, where it can find enough nutrition. Until it chopped down the whole forest, that is. And if it attacked a city, while impervious to handguns, it would still be very vulnerable to a cannon; even if not immediately lethal, an explosive round would deal enough damage that the creature is bound to die of infection eventually.

As for spitting acid, that's less effective than generally assumed. Acid takes time to corrode stuff, and living tissue has built-in protections against it. Once a guy fell into a vat of concentrated nitric acid (one of the nastier stuff as far as corrosive power goes), and another guy jumped to rescue him, and while they both remained partially submerged in the concentrated acid for minutes, they survived with bad chemical burns over their body. If your creature spit acid at something, that something would not dissolve and die; it would run away, and if it could jump in a stream it would probably get away with limited damage, and even if not, at most it would die days later as a result of the chemical burns, but hwen it's too far for your creature to eat it.

Alas, reality doesn't let us do any of the cooler stuff.

Anyway, you can improve your beast by making its shell organic. Silk is stronger than steel, and so are many other proteins and organic tissues. Kevlar itself is organic, and it could be synthesized by living organisms if they had the right enzymes. So, make the creature's armor from some proteic compound, and you can already save a lot of weight on it. Teeth are best left of metal, though; it's generally less flexible and better at cutting and piercing.

[Draginon he/him]

@king of nowhere would it having a tongue like a frog help combat the speed issue or even spinning webs like a spider? It could also have tentacles for more maneuverability to catch prey. There can also be ways to reduce the weight by having more compact muscles and hollow bones like birds, but much harder to break.

I'm not a biologist so I'm not sure how useful my suggestions are.