There’s no rule preventing the animals from drinking water.
I think this is better suited to MPSIMS than GQ.
Colibri
General Questions Moderator
El ¡ ¡ ¡ Toro!!! Strong Like Bull!!!
Humm - I’m sure you are correct - thanks for the move! 
A few possibilities:
A buzzard - flies over the stadium, stops down to eat on corpses from time to time, waits until everything is dead.
A rat - hides in a corner, scavenges on the remains much like the buzzard. Will have problems if only it and the buzzard are left; will have to hope the buzzard dies from disease.
A cockroach - will survive a nuclear war. What more need be said?
A tapeworm – best bet of all of these. It lives in an intestine blissfully unaware that there is even a death match going on. The other last survivor likely dies from disease before getting around to eating the intestine the tapeworm is in what with all the decomposing corpses all over the stadium.
I think we need different categories - I want to see bull elephant in musth versus a rhino, and I also want to see a cougar versus a honey badger.
A Tazmanian Devil vs. a Wolverine.
Sure there were. I counted a herd of about 20 elephants, two polar bears and five rhinos. All in various states of decomposition within the honey badger’s digestive system.
Does PETA know about this thread?
My money’s on the Hippopotamus.
Big
Naturally aggressive
Experienced fighter - they regularly tussle with crocodiles!
Kills on land and in the water
Fights dirty
The Honey Badger will always be my favorite underdog, though.
They don’t kill you, they tear off yout testicles. (Absolutely SFW)
If humans can’t intervene, they’ll run out of water quickly.
If we go in the spirit of the OP (which I take to mean that the victor must “win by violence”), then I’d take the bull elephant.
I think it might be fun to add weight classes, and a small lake to one part of the arena (hopefully this isn’t considered a hijack):
Open: bull elephant
4000 lbs: winner is the Hippo (this assumes part of the arena has water at least a few feet deep)
2500 lbs: winner is the Saltwater croc (also assumes a wet arena)
1500 lbs: winner is the Kodiak bear
1000 lbs: probably still a bear- maybe a Polar bear
I think it’s bears down to 500 lbs
500 lbs: Tiger
400 lbs: I’m gonna say sloth bear (according to Wikipedia, a mama sloth bear once fought off two tigers, one after the other). I also considered a silverback Gorilla.
300 lbs: Jaguar
200 lbs: Leopard
Below that is a competition between the various species of Felids and Canids, IMO. Maybe some primates like baboons, too.
I think any of the larger animals could just step on one. As long as they don’t have a break in the skin of their feet they’d probably be fine. Anything with hooves would certainly be safe.
I’m betting on the elephant.
No, no - humans can intervene - they just can’t compete. And I think a small wallow of some sort in a corner of the ring would be cool - the no water bit just means that it’s not a massive pool with sharks swimming around.
So, mostly dry ring with a wallow in one area, humans can intervene to maintain wetness in the wallow, and remove dead animals as needed (assuming they’re not eaten by the other competitors).
I’m thinking one of the large African land mammals is going to come out victorious - a big ass bull elephant in musth seems like a good bet unless somehow the big cats could gang up, despite being different species, and take him out, which I think is unlikely.
Rock, paper, scissors, Spock and a lizard enter an arena. Which one leaves?
Possibly a mongoose can bite a snakes head off, a snake’s bite can kill an elephant, but an elephant can crush a mongoose. How do you pick a winner out of those? It all depends on which animal fights which and in which order.
That’s because the elephants and bears are smart enough to stay clear of honey badgers. Think about it for a sec. People ride elephants and use them as work animals. People (well, some not too balanced people) play with bears and use them as rugs. Everyone stays the fuck away from honey badgers. And just to have a competitive advantage, honey badgers know how to use tools.
OK.
Mother elephant. When they get angry. There’s no stopping them.
There was a TV show called something like Animal Face-Off featuring hypothetical battles between assorted animals that might encounter each other in the wild. They interviewed experts and used computers to analyze biting force, etc. The African elephant beat a rhino. IRL, there was a case recently of young bull elephants killing rhinos for “fun”, because they were insufficiently socialized.
In another episode, a gorilla killed a leopard. A gorilla is big, strong, and smart, and I suspect will survive as long as many of the big cats. A chimp is smaller but smarter, so he’s going to do well, too, especially considering how agile he/she is.
I read of a case in which people put a grizzly bear and an African lion in an arena. The bear walloped the lion’s head off with one swipe. (Sorry, I don’t remember the cite.)
There was another case in which people kept sending in bulls to fight a bison. They pretty much bounced off his hide, until he got sufficiently upset. Don’t start with a bison.
What about a bacterium? Or isn’t that fair?
The gorilla hasn’t got the teeth, though - they’re very strong, but they’re pretty much limited to blunt force damage.
Those sound like some of the match ups that the Romans held in the Colosseum. Caligula had over 400 bears slaughtered there in one of his festivals. This thread would make a great Master’s thesis for some lucky zoology student. Animal fights, ancient Rome and Caligula? The paper writes itself!