This world has two continents, an old and a new. The Old World developed much as ours did, and finds itself in the throes of an Industrial Revolution. Due to the nature of the oceans and winds, transportation by sail to the New World was limited and difficult. However, with the invention of screw driven, iron-hulled ships, it becomes possible for the Old World to fully impose itself on the New. Concomitant with the Industrial Revolution is a massive expansion of population, just as happened in our world. The New World is an ideal outlet for the disaffected proletariat, and soon there are many schemes to establish colonies.
But the New World, although underpopulated by disease, is not completely empty. There exists in the New World a power unknown or forgotten in the Old: Blood Magic. A blood shaman kills a wild animal, and through a secret ritual gains the ability to mimic its power. An advanced blood shaman has the speed, agility, stamina, and toughness of a wild beast, while keeping the body and mind of a man.
The advent of the colonists caused significant tension between the few remaining natives and the newcomers. But unlike in our world, blood magic gives the natives a chance to fight back. The key to victory was the previously little-used Pampathere. Unlike the massive carapace of Glyptodon, a blood shaman using the Pampathere's armor still had the flexibility to move with the grace of a cougar and the power of a horse. But drawing on the power of the Pampathere's quarter-inch bony hide also made the shaman's nearly invulnerable to gunfire.
How does a battalion of Napoleonic Era troops kill a blood shaman?
The blood shaman has the shape and intelligence of man. But, drawing on the powers of the animals he has killed, the shaman has the mass, strength, and toughness of a bison, the agility and stalking ability of a jaguar, and the long-distance speed and stamina of a deer.
Most importantly, his skin acts as if it were a quarter inch of bone. Musket shots can penetrate, depending on the angle, but even if they do it will barely slow down a shaman with a bison's toughness.
The shaman can also call upon the best senses of the animal kingdom; a bear's smell, a wolf's hearing, a cougar's night vision, and a man's binocular, color day vision.
The shaman's enemy is a battalion of Napoleonic era troops, with all the equipment typical of that age.
The onus is on the battalion of troops to kills the shaman. The shaman wins by staying alive and conducting a guerrilla war against the colonists. He doesn't need the troops dead, per se, he can just make sure he kills a few colonists in their sleep every night to eventually persuade them to leave.