Clothes tearing is actually pretty easy if you calculate the different volumes of bodyparts (volumes get to big -> shred cloths) well given that they still exist thus for transformations between humanoids. For changing from humanoid to other things it is as tricky as wounds.
Well not all transformations heal and there where examples of body horror where the transforming person felt its bones breaking for new joints and its heart stopping to beat for a time. For insects like butterflies its not that important if they are injured since they reabsorb theyr flesh anyway so a small group of stemcells within the caterpillars body can grow into the butterfly. By modding that works too irc. you can set a certain bodypart to size 0 until it gets a growthspurt.
Also who else thought on "The beauty and the beast" as you were reading the dev-blog?
Also could we get non-monstrous stuff to create Monsters like this? It would be fitting around spherical lands where people can get "lost".
Toady did mention that we'd get tags for night creature behaviors. I kind of wonder if, and if so, how, they might work for entity creatures.
I was thinking more along the lines of curses onto a specific spot (say from a witch which was burned out of superstition) that turns a entire village in Nightcreaturish things or certain certain circumstances in a spherical land turning you into one - say Rorec McHuman tuning into a Bear after eating the wrong fruit/animal.
Bug prediction: FBs and or titans will by glitch use the same reproducing rules as the Nighters which ends with a family of *big spiders made of fire with steel feathers which mutter the names of theyr victims. Beware of its webs.* things inviting themselves to your fort.
Btw can FB and demonwebs be harvested for silk? If yes how much are they worth?