Here is a link to that post Doppelgangers
I made this as a sort of representation of doppelgangers.
Made using Daz Studio and Gimp.
The picture is kind of a representation of that and of how I imagine them looking when they shift forms.
I had fun experimenting with this one, I would love to work on some more Dopplegangers
If you’re referring to my game project that the picture is for then yes there are some limits.
They are considered Medium sized creatures and although they can take shapes of aliens and even the insectoid races they can't reach a size to be considered a large creature, or even a tiny creature. Past that they can pretty much mimic any creature in their size range; honestly that makes them pretty powerful in the setting, although they are not a playable race and are rare as NPCs.
Yeah I put a link in the description to a post I made about the doppelgangers on my blog for my tabletop homebrew game project.
Still working on it, but I've got enough down to actually play the game which is fun.
And yes going from normal humanoid form to an insectoid form takes longer than them shifting to another type of humanoid form. So it's doable but more of a process and time involved.