Ironscale Hydra

What krakens are to The Sea and Dragons are to The Sky, Hydras are to the lands of Theros. Various Hydras dwell at the fringes of civilization, from the bog-dwelling Hydras known across the multiverse to massive ironscale Hydras that lurk in deep wildernesses. Beyond even these exist serpentine horrors born of the whims of foul gods, like the legendary hydra Polukranos. Territorial Terrors. During their early years, Hydras feed their rapid growth by terrorizing the land. When they grow large enough, they look for a territory to claim as their own. Often, they steal lairs from other Monsters in prolonged, devastating battles.
Vicious Growth. Soon after a hydra claims a territory, it typically buries itself, entering a period of hibernation during which it continues to grow. When it awakens, it goes on a feeding rampage, so Beginning the cycle once again. These rhythms of destruction sometimes become so ingrained in the minds and lore of a people that, even after a hydra's defeat, the beast might reappear as a Nyxborn being and begin its legend anew.
Five-headed ironscale Hydras lurk in the wild places of the world, being Common foes for heroes seeking to test their mettle against terrors worthy of the gods' notice. Most ironscale Hydras inhabit lakes and boggy caverns, from which they hunt unwary creatures that come for a drink or swim.