10 lions (3males) vs polar bear
Jaguar vs two wolves
Siberian tiger vs wild boar
Jaguar vs warthog
Baboon vs pit bull
6 wolves vs warthog
Gorilla vs hyena
450lb anaconda vs hyena
Bull Elephant in musth vs T. rex
350lb reticulate python vs wild boar
20ft African Rock Python vs warthog
Tiger the size of T. rex vs T. rex
Grizzly the size of T. rex vs T. rex
10 Lions (3 males) vs Polar bear: The polar bear will weigh almost as much as the 3 male lions combined, but it will be in trouble here. Polar bears are immensely powerful & are accustomed to dealing with large adversaries (walruses, muskox, seals, etc.), but it would be overwhelmed by 10 lions. Lions are terrific at teaming up to conquer large, dangerous animals (Cape buffalo, giraffe, eland, etc.), and would eventually overpower the bear by sheer numbers. The polar bear will probably injure some lions early on in the battle (with bites & paw swipes), but it won't last long. The 3 male lions by themselves would actually have a chance to defeat the polar bear without the help of the 7 lionesses. 10 lions win.
Jaguar vs 2 Wolves: The jaguar will weigh more than both wolves combined. Wolves are great at teamwork (and have better endurance than big cats), and they will likely attack from opposite sides to throw the jaguar off-balance. Jaguars are very powerfully-built felids with fast reflexes & impressive weaponry (strong jaws that can crush skulls/sharp claws). The jaguar will probably use its quickness to capture one of the wolves as it moves in close, and its ability to seriously injure the canid in a short amount of time will give it a good chance to make this fight a one-on-one. The jaguar is too formidable for 2 wolves to deal with (2 wolves would likely be on par with a leopard or a puma). Jaguar wins.
Siberian tiger vs Wild boar: The Siberian tiger will weigh approximately 50% heavier than the wild boar. Siberian tigers are accustomed to hunting wild boar, and can use their front paws to quickly neutralize the head & shoulder area of the suid (and use its jaws to finish the battle). Wild boars are always dangerous prey items (tough hide; sharp tusks), but tigers are equipped to deal with them. I would favor a tiger at parity as well, but the level of danger would certainly be higher for the big cat. Siberian tiger wins.
Jaguar vs Warthog: The jaguar will be slightly heavier than the warthog. Jaguars have the assets most big cats share (quickness/agility/jaws & claws/finishing know-how), and are widely considered to be the strongest felid pound-for-pound. They also have a unique killing method (crushing the skull or spine with its vice-like jaws) that serves them well, and their stocky, muscular builds enable them to excel against most low-to-the-ground adversaries. Warthogs are nimble animals with long, curved tusks used to defend themselves. They can seriously injure an attacker with a slash of these tusks, and it will be important for the jaguar to gain control of the warthog's front end with its front paws to avoid this. The jaguar will need to be cautious, but it has the weaponry & know-how to succeed here on most occasions. A jaguar might be driven away in a realistic encounter, but should prevail if determined to battle to the end. Edge to jaguar.
Baboon vs Pitbull: This battle would depend somewhat on which species of baboon is used & whether or not the pitbull is game-bred or not. American pitbull terriers can be formidable fighters. These dogs have tons of energy, and will battle through injury with great intensity. Game-bred pitbulls will attack immediately, and will attempt to latch onto their targets with their strong jaws (usually aiming for the head & face area; many times using a bite & shake" method). Baboons are mobile, agile animals with the advantage of hand usage (which can help dictate the positioning of the battle). Where the APBT latches on is important to the outcome. A bite on the head or face area of the baboon will likely seal its fate (as it won't be able to counter-bite), but a misplaced bite (due to the baboon's defense with its hands & mobility) will enable the primate to repeatedly sink its long upper teeth into the body of the dog (causing quick, deep injuries). A regular pet pitbull would likely have its hands full against any baboon in its weight range, but a game-bred APBT can defeat many animals larger than itself. Assuming the APBT we use here is game-bred, it will take the larger species of baboons to compete with it. Chacma & olive baboons will weigh anywhere from 25-35% more than the APBT, and will have a decent chance to prevail about half the time. The mandrill can weigh 50% more than the APBT, and will probably defeat the canid most of the time.
6 Wolves vs Warthog: Each wolf will only be about 40% of the warthog's weight, but the pack will have a decent chance here. Wolves are great at teamwork, and will attack from all sides (darting in & out with bites) until a couple of them can clamp onto the warthog (one in front; one in back) to immobilize it. Once they do this, the rest of the pack can join in to finish the job. Warthogs can make quick left-to-right movements to slash with their tusks, and the chances of the wolf pack sustaining injury is great. If the wolves are wary of the tusks, they should be able to wear the warthog down. The warthog might slash a wolf or 2, but it won't overcome all 6. 6 wolves win.
Gorilla vs Hyena: A gorilla will weigh 3 times as much as a spotted hyena, about 4 times as much as brown hyena, & almost 5 times as much as a striped hyena. Spotted hyenas have durable builds & powerful jaws, but not even they are a match for a gorilla one-on-one. The strong arms & hands of the gorilla will easily control the positioning of the battle at close quarters where the primate can utilize its bite. The hyena might get a bite in at the onset of the conflict, but the gorilla will use its strength to overpower the smaller animal. A hyena will need help from other members of its clan to defeat a gorilla. Gorilla wins.
450lb Anaconda vs Hyena: This huge anaconda will be almost 3 times as heavy as the hyena (assuming it is spotted). Hyenas have strong, bone-crushing bites that help them to subdue a variety of prey items (as well as dismantle a carcass), but it will need to be very careful when trying to attack an anaconda. Anacondas can strike quickly to latch onto a target (with many sharp, backward-pointing teeth), and will use this bite to create an anchoring point as it moves its coils toward the intended victim. The spotted hyena is somewhat ungainly, and will not be able to easily avoid the anaconda's strike as it tries to deliver a bite of its own. If a hyena is grabbed by the anacondas jaws, it will have to struggle mightily (and counter-bite) to free itself, and it won't be able to do so if the coiling process becomes too advanced. If the hyena stays away from the anaconda's head & delivers multiple bites, it can wear the snake down and eventually kill it. However, the chances are slightly greater that the stronger anaconda will prevail. The hyena would be in serious trouble in shallow or deep water. Edge to anaconda.
Bull Elephant (in musth) vs T-rex: The Tyrannosaurus-rex will weigh about 33% more than the elephant (if we use an African one). A typical meeting between these 2 would likely rattle an elephant (never having seen a T-rex before), but an elephant in musth would probably charge with reckless abandon. Tyrannosaurus was believed to be a skillful hunter of large quarry, and used it enormous jaws & blade-like teeth to remove large chunks of flesh from victims. The dinosaur would probably readily engage the smaller elephant, and would immediately bite when the pachyderm came into range. An elephant's charge might stun or topple a T-rex on occasion (and its tusks might stab into the theropod), but the likelihood is greater the predator will overcome the herbivore with its massive bite. With the Tyrannosaurus accustomed to dealing with ceratopsians (that have long horns & protective neck frills), the elephant will be a step down. Even the elephant's musth-induced ferocity won't be enough to overcome a Tyrannosaurus on most occasions. Tyrannosaurus-rex wins.
350lb Reticulated Python vs Wild boar: The wild boar will weigh more than 25% more than the python. Pythons are excellent ambush hunters, but are poor fighters on land when face-to-face with a large opponent. The python is certainly capable of constricting a wild boar, but it will have trouble pulling this off without a surprise attack. The wild boar's sharp tusks can slice open the python, and the suid's tough hide might make it difficult for the constrictor to latch on securely with its jaws (to create an anchoring point) without the struggles of the boar pulling it off. The python's endurance on land is quite poor, and any prolonged struggle will render it unable to continue any offense. The wild boar will be in trouble if it allows the coiling process to start (it won't be able to free itself), but should have enough mobility & weaponry to defend itself from this. A reticulated python would fare much better in shallow water (where its mobility & endurance will be greatly improved), and would probably succeed in overcoming the boar more times than not. On land the odds are against the python. Edge to wild boar.
20ft African Rock Python vs Warthog: The warthog will weigh approximately 50% more than the African rock python. This fight will be similar to the reticulated python vs wild boar. Rock pythons are aggressive, capable hunters, but have the same limitations on land shared by all large constrictors (poor mobility & endurance). The warthog will be mobile enough to mount an offense with its tusks, and will be large enough to struggle effectively as the python attempts to bite & coil it. The python can win by ambush or with the benefit of water, but will have trouble subduing a warthog face-to-face. Edge to warthog.
Tiger (the size of T-rex) vs T-rex: A tiger weighing the same as a Tyrannosaurus-rex will have a shoulder height about 55% the height of the dinosaur (if the dino stands upright). The tiger will have the advantages of quickness & agility, and will have the power to leap onto the T-rex & drag it to the ground. Even if the tiger doesn't topple the T-rex, it will be able to get into a position that enables it to employ a throat bite while avoiding the jaws of the theropod. The tiger won't avoid the Tyrannosaurus' huge bite everytime, but should have the reflexes to avoid it most of the time. Close fight, but the tiger has the edge.
Grizzly (the size of T-rex) vs T-rex: A grizzly bear weighing the same as a Tyrannosaurus-rex will have a shoulder height about 55% the height of the dinosaur (if the dino stands upright). The grizzly's ability (or inability) to avoid the huge bite of the T-rex will be key in this battle. The grizzly bear is probably the most formidable bear pound-for-pound, but the Tyrannosaurus is perhaps among the most formidable of the theropods. The grizzly bear will have endurance & paw usage as its chief assets, and it has the strength to wrestle the Tyrannosaurus to the ground in a close-quarters engagement. However, the bear's lateral quickness isn't as great as the tiger's, and it won't be as successful as the big cat when it comes to avoiding the damaging bite of the dinosaur. Both can win here, but it seems the Tyrannosaurus has better means of causing greater injury early on than the grizzly bear does. Close to 50/50; slight edge to the Tyrannosaurus-rex.