A couple ideas I've gotten from reading this thread:
First of all, diseased units ought to have some small chance of infecting other units-maybe by touch attack alone? This could make having undead who are diseased actually slightly beneficial. The reason this would be cool is because you could then use it strategically, by intentionally infecting weaponless undead. Obviously, this would be easy for C'Tis.
Secondly, Miasma should go deeper than just a disease effect. What if it occasionally summoned random attacks on enemy units under C'tis domination? Something like the 'Illwinter' spell, but with crocs/alley-gators, snakes, poison toads, vinemen, etc. Maybe some more interesting units in there too-like a tribe of pygmies with poison arrow archers and big elephant-spitting spears, or the occasional rampaging dinosaur, or swamp witches and their pet swamp demons, undead blood-drinking tree spirits, etc. Maybe also a chance for a random casting of Rain of Toads.
They also might get access to a different version of Fairy Court: the Unseelie Court, which-instead of a healer queen, has a Queen of Air and Darkness with stealth, cause unrest, and ofcourse access to Air and Death.
There could also be swamp trolls, and a swamp troll king.
Does C'Tis have it's full regimen of heroes? If not, how about a heroic man-eating crocodile named 'Gustave'? And maybe some multi-hero blood druids?
They might even reasonably have an undead (fossilized?) Purussaurus (or maybe just an immobile fossilized skull, with some specialized power?) as a Pretender.
Purussaurus was a relative of the modern Caiman that reached 12 meters in length and was enormously broad, with a truly massive skull. It existed only 8 million years ago.
http://scienceblogs.com/tetrapodzool...er_caimans.php
By the way, the largest known (measured) living crocodile in the world lives in Australia and is over 25 feet long.
The aforementioned 'Gustave' (Spoiler: the basis for the film 'Primeval'), a Nile Crocodile, who lives in Burundi, Africa, is estimated at atleast 20 feet long, as much as 30 feet, weighs atleast a ton, and is believed responsible for over 300 human deaths. I can't find evidence of any alligator exceeding a ton in weight (although the largest captured weren't generally weighed, and may have exceeded a ton in weight), or 20 feet in length. The largest ever recorded was 19 feet, 2 inches long, but wasn't weighed.