Symbolism, Imagery, Allegory
"Some Nightmare Tadpole"
There's no way around it: it's definitely weird that Octavian wants to wear a dragon's skull over his head—and that he "cried and sobbed until they allowed [him] to sleep in the room with the monster" (1.6.13). But you know how symbols work, Shmoopsters: When something catches your eye—which the dragon skull most certainly does—it's usually trying to tell you something beyond what meets the eye.
So why does Octavian want that skull on his head? We think it has something to do with what he imagines he looks like with the skull on:
[…] my head in its long-rotted cranium, my body curled behind it as if it and I were some nightmare tadpole waiting to burst from the murk and reinstate its reign upon the genteel fields of Earth. (1.6.13)
Note the use of the subjunctive here—"as if it and I were." This is basically a blatant way of introducing an imagined impossibility. In other words, Octavian will never actually be "some nightmare tadpole waiting to burst from the murk" because he's human—but that doesn't stop him from imagining becoming what the skull makes him look like.
Think of it like dressing up in a costume for Halloween so that you can go around scaring people. You'll never actually be a scary witch or Frankenstein, but isn't it cool to pretend? And if you spend your days feeling kind of invisible or investing in politeness, the chance to scare people might even feel pretty thrilling and powerful. When Octavian wears the dragon skull, he imagines being born again as a powerful creature—a creature who can reign, instead of being reigned over the way Octavian always has been.
How the Tadpole Becomes a Frog
His vision is also kind of like a coming-of-age story. Young Octavian is like that tadpole just waiting to "burst from the murk" and become the adult frog that can "reinstate its reign upon the genteel fields of Earth." That, by the way, is also some heavy foreshadowing, even if Octavian doesn't exactly "reinstate [his] reign" over Earth—he does learn to fight, to go from tiny tadpole-boy to a grown young man who escapes his slave-masters twice. That takes some serious guts.
"Survival Through Adaptation"
If you're a biology buff, there's also a slight whiff of evolutionary theory floating in the imagery too. After all, at the heart of the symbol is the transformation between tadpole and a creature who walks the earth. While it's dangerous to have biology and race hang out too closely together—after all, these are the very basis of Octavian's childhood as an enslaved science experiment—we can understand the evolutionary transformation referred to in the excerpt above as a sort of reclaiming of the ways in which science is used against black people, and Octavian specifically.
In other words, if people want to treat Octavian like a living experiment, a human specimen, then he is claiming himself as a model of evolutionary success—someone who goes from a nightmare to ruling the earth.
Not convinced? Consider this: Cassiopeia later recalls how Octavian responded to her when she teased him about how the skull might bite him. According to Cassiopeia, he said "'Do not be afraid, Mother. Know you whose skull this is? Mine. I would not bite my own self'" (1.26.158)—in other words, Octavian already is as powerful as a dragon. He is just waiting to "burst from the murk" still—but when he does, well, look out world.