-Hi! I'm a pufferfish. I'm about the size of a baseball, but when threatened, I expand my stomach by filling it with water, puffing myself up to the size of softball and exposing my pointy spines, injecting anyone who would eat me with deadly tetrodotoxin. A few predators are resistant to it, but even if the poison can't hurt you, you still have a mouthful of internal puncture wounds. Nothing kills me and gets away scot-free.
-Silly fish! You think you're badass? I'm a poison arrow frog. I'm only about half the size of a golf ball, but my body contains enough poison to kill you and nine of your favorite friends, and that's batrachotoxin, which makes tetrodotoxin looks like a walk in the park. I come in all sorts of vibrant, don't-eat-me colors to make predators know that I am not to be trifled with. Oh, and that batrachotoxin, the one that's more than 150 times as lethal as your silly tetrodotoxin? It's named after me.
-Foolish amphibian! And foolish fish! You think you're so impressive with your bones, and your reliance on a single form a toxin? I am the deadly blue-ringed octopus, most badass of them all! I'm about the size of a golf ball, but not only do I possess all the usual octopus abilities, but when threatened, I light up the dark blue spots on my body to bright blue spots, and if that doesn't ward you off, I bite- injecting you with both batrachotoxin and tetrodotoxin, so even if you're totally immune to one of them, you're still screwed. None are more badass than I am!
-That's what you think, dear little mollusk. But I surpass even you, for I am a box jellyfish. I am far larger than any of you, with tentacles that can reach ten feet in length, and unlike most of my jellyfish brethren, I can actually swim, controlling my movements. Those tentacles are covered in venom-injecting stingers, by the way- stingers with a response time measured in nanoseconds. If you brush up against one of them, you'll have been stung before the nerve signal that you've touched something even reaches your brain. For brains, you see, are a sign of decadent weakness, needed only by those who can't fend for themselves. I have twenty-four eyes, more than all of you combined, and I don't need anything as banal as a brain to process the images I receive from them. Plus, lacking a brain, I'm completely safe from a zombie uprising, even an aquatic one! So you see, nothing could be more- hey! I'm monologuing here! Who the hell are you?
-I'm a human being. I'm roughly the size of a human being. I am significantly larger than most animals, but even among my similarly-sized peers, my musculature is absolutely pathetic. My size does impart me with some resistance to a great many toxins, but I have none of my own. I have no horns, no scales, no spines or spikes. I do technically have claws, but they're not sharp enough to cut or pierce anything, and aren't strong enough to be used in fight anyway. I have the frontal teeth of a predator, but lack the jaw strength to kill anything that's calorically worth my time. I have the back teeth of an herbivore, but lack the digestive equipment needed to break down cellulose. I'm a bipedal animal that walks upright, but I don't even have a tail! What I do have is an impressive array of tricks: speech; shoulder joints designed for accurate, long-distance throwing; opposable thumbs; the capability to derive sustenance from an incredibly wide range of sources, and a brain sophisticated not merely by mammal standards, but primate ones. These tricks give me the capability of carving out a solid ecological niche and surviving quite well within it. But that's not what I did. What I did was to spread out over every point on the surface of the Earth and become the dominant life-form.
And how did I do this, given all the weaknesses listed above? By means of the one strength I didn't mention: I am completely, and totally, out of my mind. I poison my own food, air and water to weed out the weak! I set off fission bombs in my only biosphere! I regularly attempt major genocides against my own species! My highest-ranked god descended from on high, said "knock it off with the violence", and I nailed him to a stick! I am feared by every single fear-capable creature on this planet, and I have started multiple space programs to leave the Earth and reach the rest!
