I love the idea of Hydra getting hold of a Bauk who can shapeshift into a man, using it to kill people who get in their way and sow terror amongst their enemies. Deaths caused by something obviously inhuman, bodies torn apart by teeth and claws inside locked rooms. However, it gets more and more feral the longer it's been captured and eventually they have to lock it away so it doesn't exact revenge on them.
Steve and the rest of the Avengers are investigating an abandoned Hydra base in Serbia, when they stumble upon this man chained up and rescue him only to find out that he can change into this creature from local mythology. Them working together to take out the remnants of Hydra, and the Bauk being named Bucky since Hydra only ever called him the Asset or the Beast.
"The Bauk is said to be an ungainly, hulking creature, its form a patchwork of primal terror. Its most defining features are its razor-sharp claws, gleaming like obsidian in the faintest light, and a shambling gait, a motion so clumsy it seems at odds with its calculated lethality. Stories often describe it as shrouded in impenetrable darkness, its body merging seamlessly with the gloom, making it nearly impossible to discern until it is far too late. The creature’s name itself is an onomatopoeic echo of its nature—a low, guttural bau that chills the air and curdles the courage of anyone who hears it.
Legends tell of the Bauk’s unsettling preference for desolate and forgotten spaces. Abandoned houses, deep forest glades, and the mouths of shadowy caves are its hunting grounds, places where the boundary between the world of the living and the domain of the unknown grows perilously thin. Here, it waits in eerie silence, a predator of patience. Its origin is a matter of conjecture—some say the Bauk emerged from the primal fears of ancient people, a living warning about the dangers of straying too far into the dark. Others suggest it may be a relic of the natural world itself, a distorted memory of the bear, now lost to much of Serbia but living on as a phantom in the collective mind.
A tale often shared by elders is one of the hapless wanderer—a foolhardy soul who ignores the warnings of the village to take a shortcut through a Bauk-infested forest. The tale always ends predictably: the Bauk, with its supernatural ability to vanish into the shadows, ambushes the traveler, its massive claws paralyzing the victim as they are dragged into the beast’s lair. The screams, sharp and brief, fade into the quiet, leaving behind only the sobering reminder to respect the darkness." - Gods and Monsters
