1) 500kg nile crocodile vs 800kg kodiak bear (in 2m deep water)
2) 500kg nile crocodile vs 220kg lion (on land)
3) 11t spinosaurus (new 4 legs version) vs 6t ankylosaurus
4) 11t spinosaurus (new 4 legs version) vs 4x 1600kg arctotherium angustidens
1) 500kg nile crocodile vs 800kg kodiak bear (in 2m deep water): Nile crocodiles are much more effective combatants in water than they are on land. On land, stamina and mobility can be definite limitations for a crocodile, but in water those liabilities are removed. A Nile crocodile is a very strong animal with an armored hide (covered in osteoderms, or bony growths), vice-like jaws, and a powerful tail that aids in movement through the water. It can grab large animals at the river's edge and pull them under to drown. A Kodiak bear is a large mammal that frequently ventures into water to hunt for fish, and it is armed with huge claws and a formidable set of jaws. The Kodiak bear has great strength and endurance as well. An 800kg Kodiak bear will be about 1.6m at the shoulder, and it won't be able to easily touch bottom in 2m of water without being submerged under the surface. The Kodiak bear's offense (swiping claws, forelimbs used to grab and control movement, biting) won't be effectively employed in 2m of water, and its advantages in strength and endurance will be minimal. The Nile crocodile probably won't attempt an attack on the bear in a realistic scenario considering the mammal's weight advantage, but it will be much more at home in the water. American alligators have received injuries from attacks on swimming American black bears, so it's plausible to assume the Kodiak bear will have the means to inflict injuries on the Nile crocodile even in 2m of water. Zebra and wildebeest that are attacked by Nile crocodiles in the Mara river sometimes escape, and they are probably less capable of defending themselves from the reptile's attack than a Kodiak bear will be (and the bear, being stouter, will have fewer areas on its body for the crocodile to secure a solid grip with its jaws). The Nile crocodile probably won't be able to complete a kill on the larger bear before the bear's resistance drives it away, but the bear will have a slim chance of dispatching the crocodile without being able to base its weight on solid ground. A stalemate is the most likely result in an encounter with these 2 animals in this setting, but the crocodile will be a little safer overall than the bear will be. Edge to Nile crocodile (great question, by the way!).
2) 500kg nile crocodile vs 220kg lion (on land): On dry land is the only place a 220kg lion will have a chance to defeat a 500kg crocodile. These animals often encounter one another, and mutual avoidance is the usual result. Lions won't actively predate upon crocodiles, but they will drive the reptiles away if they threaten young ones or attempt to steal a kill the lions have made. A lion crossing a river with crocodiles therein is at great risk of being seized and drowned, and lions will typically avoid putting themselves in situations like that. A Nile crocodile isn't nearly as formidable a combatant on land as it is in the water, but it's no pushover on land. It is limited in regards to mobility and stamina, but it can still make quick movements in short bursts and battle violently for a short time. A lion will have trouble breaching the armor-like hide of the crocodile, and it will be in trouble (even on land) if it is caught in the crocodile's jaws. Tigers and jaguars are more adept than lions at dispatching crocodilians, but a lion can pull it off if it's careful. It is imperative for the lion to wait for the crocodile to fatigue before the cat attempts to make physical contact, and it may be able to accomplish this by utilizing its quickness and agility to stay out of harm's way while making the crocodile expend energy by making the reptile believe it needs to do so to defend itself. In a realistic encounter the lion will growl and swipe at the crocodile to drive it away, and the big cat won't initiate a serious attack unless it is absolutely necessary to do so. The lion will have the advantages of stamina, mobility, and speed. The crocodile will have the advantages of strength and durability (armored hide). Assuming the lion is one experienced in dealing with crocodiles and is familiar with their capabilities, it will have the slightest of edges on land. Close to 50/50; slight edge to lion.
3) 11t spinosaurus (new 4 legs version) vs 6t ankylosaurus: Complete fossils of Spinosaurus have yet to be discovered, and the bipedal version of these creatures is still widely accepted. Having a 4-legged stance won't greatly alter the effectiveness of Spinosaurus as a combatant. Spinosaurus had large claws on its forelimbs that were likely used to help it in catching the aquatic animals it fed on, but these would make decent weapons as well. Spinosaurus' bite wasn't nearly as strong as the bite of many large theropods, and its conical teeth were designed to seize and hold fish. Ankylosaurus was a widely-based 4-legged herbivore with heavy armor upon much of its body and a tail club of bone for swinging at enemies. A key factor of this battle will be what each animal is accustomed to doing (despite what they look like they may be able to do based on their physical appearance). Spinosaurus did not predate upon large terrestrial animals, and wasn't practiced at breaching the defenses of armored ones. It's unlikely Spinosaurus would make a competent attempt to "flip" the Ankylosaurus with its forelimbs or use its length and better mobility to safely avoid the swinging tail club of the Ankylosaurus. Ankylosaurus was very practiced at dealing with large, dangerous theropods (like Tyrannosaurus), and could defend itself aptly on many occasions by crouching low and swinging its tail at the legs (or lowered heads) of its attackers. If these 2 animals lived together and were adapted to forming the best strategies and making the right decisions during each encounter, the Spinosaurus would likely have the physical attributes necessary to be favored (perhaps heavily) in such a battle. As it stands now, the Ankylosaurus will have a much better idea of how to effectively deal with the Spinosaurus than the other way around. Without the knowledge and experience to flip the Ankylosaurus over (or form some other strategy to dispatch it), the Spinosaurus won't easily be able to make a meaningful assault without putting itself at risk. Despite the Spinosaurus' inexperience in this matchup, its great size advantage (its height at the hips will be double the Ankylosaurus' height) and better mobility can't be discounted. Close to 50/50; slight edge to Spinosaurus.
4) 11t spinosaurus (new 4 legs version) vs 4x 1600kg arctotherium angustidens: The Spinosaurus will weigh over 6 times as much as each Arctotherium (almost 7 times as much if the tons are metric tons). Arctotherium was perhaps the largest bear ever to exist, and was kin to the modern-day spectacled bear (9 times as heavy, though). It was close to 2m at the shoulder, and was likely a scavenger as well as a hunter. Bears have great strength, endurance, and good weaponry (jaws, swiping claws). It's unlikely the Arctotheriums would know how to work together in this battle, and they would be too small to make much a dent in the much larger Spinosaurus with their offense. The bite of Spinosaurus wasn't nearly as powerful as the bite of, let's say, Tyrannosaurus, but it was still powerful enough to dispatch an Arctotherium without too much trouble. For a weight perspective, imagine 4 giant pandas trying to tackle a huge saltwater crocodile. The Spinosaurus is simply too big here. Spinosaurus wins.