This thread is giving me so much life right now lol. 
I feel like @Fornjotr fern would fit perfectly in a swamp setting. Those fireflies Bruno has are great. So animal wise maybe snakes, turtles, lizards, frogs, gators, maybe a heron type bird. I’m sensing an influx of snakeskin furniture on the horizon lol. If you’re looking for a new race of monsters for the swamp maybe go with lizardfolk or some kind of mutant bird folks like the Skeksis from The Dark Crystal.
EDIT: OMG I just saw [MOD] Ballista turret - updated Jan/15/2017 [1K Downloads Yay!] @Hyrule_Symbol has some amazing Sylph models that could probably get some claws, bird feet, and color changed to look like harpies! With permission of course lol.