For the next release I will focus on the following things :
 * Tileset update
 * Megabeast/Semimegabeast update
 * Addition of several exposed, megabeast/semi-megabeast, and a few animal graphics.

Ever since I had to remove the Smokee I've noticed the extreme lack of megabeasts in Corrosion. So I will be working on adding some more, I already have a few ideas. I will also be adding graphics.

In Vanilla Dwarf Fortress, there is very little difference between a semi-megabeast and a megabeast. Why is a roc, a giant bird, a megabeast while an ettin, a giant with two heads, a semi-megabeast? So in Corrosion I will differentiate them more. If you turned one of my megabeasts into a semi-megabeast you should notice the difference.

Semi-Megabeasts are going to have long descriptions that tell you exactly what they will do. They should be able to mow down your unprotected civilians that are outside. However a small team of competent, well armed and armored troops should have moderate to little trouble dispatching these creatures. Thus they will arrive earlier then megabeasts. In a nutshell, they will be larger Infected plus unique abilities. They can all avoid traps.

Megabeasts are going to be much more unique. They will not always be infected, and will require much more thinking to deal with. Their descriptions will be vague and won't tell you exactly what they do. They'll tie into the story, but they'll be more like science fiction creatures.