The Nile croc is the largest in the world-it's estimated that they could get up to 30 feet long, potentially. That's dragon-sized.
Are there Will O' The Whisps in the game?
I'd like to see more done with bog mummies-and specifically Jotun-sized bog mummies, since there's real-world evidence of actual giant (6'6 +) redheaded humanoids living in prehistoric times, or possibly more recently, and ending up in swamps.
A nation of Jotunesque bog-mummies would be awesome.
Were-boars or a race of humanoid boars would make for cool swamp monsters.
Lots of fish and salamanders live in swamps-real life salamanders in Asia get up to 6 feet long. And there's urban legends about catfish growing to the size of a bus!
Good inspiration for aboleths, so maybe there's a less intelligent, but still dangerous, amphibious version?
How about Swamp Thing? Not only do the comics provide lots of monstrous inspiration, but it'd be cool to have, say, an independent heroic, stronger and more intelligent version of a Vine Ogre, with lots of Nature magic, named "Swamp King", performing basically the same function as Bogus, only for nature-related events.
When talking about albino crocs, don't forget the urban legends about albino crocodiles living in the sewers of New York.
Hippos are very dangerous, but I'm pretty sure that they wouldn't stand a chance against a full grown bull African elephant. For that matter, the Ratel, or "Honeybadger", is considered, pound-for-pound, the most dangerous mammal in Africa.