I agree that its easier to list the animals you CAN’T beat. Here’s a partial list, divided into categories:
Gorilla, Chimp, Orangutan. Much much stronger than humans, and faster too. They also negate the biggest advantage an unarmed human has, grappling, since they can grab ahold of you with four hands, and then bite the hell out of you. Other monkeys and apes are just too small, you’d win against them.
Elephant. You’re dead, obviously. Trunk, tusks, feet, weight, intelligence. Forget it.
Rhino, Hippo, Giraffe, Cape Buffalo, Wild Boar, Horse, Zebra, Bull, Bison, Moose, Elk, plus a few others. Any sufficiently large hoofed animal is going to clean your clock unless you get really lucky. Any hoofed animal that outweighs you by more than 3-1 is a long shot. They are extremely fast runners, and many could kill you with one kick. Your only advantage is your turn radius…you might be able to dodge a charge just in the nick of time. Do this often enough and the animal might tire, and you might be able to choke it as mentioned above. But all it takes is one split-second mistiming and you’re dead. And many of these animals are fast enough that you won’t be able to dodge anyway, or smart enough to WALK you down instead of charge.
Crocodile, Alligator, Caiman. If you’re in the water, you’re dead. If you’re at the water’s edge, you’re dead. On land you have a chance. The secret is that their jaw closing muscles are incredibly powerful, but their jaw-opening muscles are pretty weak. You can literally hold their jaws shut with one hand. If you can hold the jaws shut, you might be able to somehow choke them. But the trouble is that they don’t need much oxygen, and their tails can knock you off your feet, and their hide is pretty much impervious to bites, gouges or punches. Not much hope.
Cassowary, Ostrich, Emu. Probably the only man-killing birds, although a diving eagle might get lucky and break your neck. Thier weapon is the disemboweling kick. The disemboweling kick, and tremendous speed. Make that, their weapons…
Any big shark or marine mammal, larger than you. Assuming you are swimming they would tear your ass UP. Nothing you can do, except MAYBE a lucky bash on the nose. But what next? You can’t get any leverage, you can’t catch them, you can’t hold your breath for more than a minute. Anything twice your size and you’re dead.
Next, poisonous or noxious creatures. Poisonous snakes are pretty easy to kill…if you have a stick. Otherwise, a crapshoot. Some people are experienced enough to grab them by the back of the head, once you,ve done that you’ve won. But how about a porcupine or hedgehog? With a stick or a rock, easy to kill. But with your bare hands and feet? Not much hope, although they can’t hurt you much if you keep your distance. Poisonous arthropods are generally not much danger, just squish em, they can’t run faster than you. You might want to stay away from electric eels, stingrays, large jellyfish, and pufferfish. Again, not much they can do against you, but if you touch them you are going to pay. With a simple tool, they are dead, but with bare hands you can’t do much.
Last, the carnivores. Any bear, even a small bear, and you’re dead. They are super strong and pretty much invulnerable to any bare-handed attack you could pull off. A spotted hyeana will probably kill you, but a brown or a striped hyeana is probably too small. You could probably take on a wolf bare-handed. If he knocks you off your feet you are in trouble, but if you can grapple him you can choke him to death. Any smaller canid can be handled similarly. A wolverine will tear your ass UP. An american badger or a honey badger would do some major damage, but you’d probably kill him in the end although maimed for life. Other mustelids are probably safe to attack. I don’t think you’d be in trouble from any viverrids or procyonids, although you’d suffer nasty bites. That leaves the cats. Any cat half your weight or above will probably kill you. Grappling a cat would be problematic, since they will rip you with their backfeet. Goodbye small intestine. If you could somehow get them in a chokehold you might have a chance, but any cat over half your weight is going to be amazingly strong, fast, and agile. Many cats routinely kill prey many times their size. Anything bigger than a bobcat would probably kill you. Lynx, cougar, lion, leopard, jaguar, snow leopard, or tiger, say goodbye. Cheetah, caracal, clouded leopard, ocelot, serval, or anything in that size range and you have a fighting chance, although I wouldn’t give you more than 50-50 odds.
Other than that, kill away.