I'm going to be introducing my party to Mimics shortly and whenever I add in a new monster I like to adjust them so that they fit into my campaign but also fit my personal preferences. I also sometimes like to create templates for myself that will allow me to quickly and easily make another version of that creature at a different challenge rating or of a different type, etc...

With Mimics, I've decided that I don't want every mimic to be able to copy the properties of any item. I want the Mimic's abilities to be largely biological in this campaign, not magical, and as such I don't think a mimic that can take on the appearance and texture of wood, would also be able to convincingly take on the appearance and texture of stone. So I'm making different strains of Mimic and I need help determining what mechanical difference to give each strain to set them apart. I know I want to base their AC on the material they mimic. Here's what I have:

Paper Mimic (Mimics scrolls, books, letters, etc...) - AC 11, Fire Vulnerability, +2 Intelligence, Possible 1/day spell casting if mimicking a spell book
Cloth Mimic (Mimics clothing, tapestries, etc...) - AC 11, +2 DEX, Acid Resistance instead of Immunity, Fire Vulnerability, 15ft Climb Speed, Stealth Expertise?
Glass Mimic (Mimics glass figurines, window panes, etc...) - AC 13, Translucent (Whatever that matters for), Bludgeoning Vulnerability?, After taking a large enough single hit the mimic becomes "shattered"?
Wood Mimic (Mimics wooden doors, chests, etc...) - AC 15, Fire Vulnerability
Bone Mimic (Mimics bones, teeth, antlers, etc...) - AC 15,  Bludgeoning Vulnerability
Stone Mimic (Mimics stone doors, statues, etc...) - AC 17, -2 DEX, Fire Resistance, -5 ft speed
Metal Mimic (Mimics metal grates and doors, armor, etc...) - AC 19,  Fire Immunity

You get the idea. SO what kinds of properties should I give these mimics depending on their strain? The idea is I create a mimic of whatever CR I want and then I just tack on the strain effect to finish it off. Any help is appreciated.

Wood: Standard stats, some fire vulnerability depending on the type of wood

Cloth: Dex increase, acid resistance instead of immunity, climbing, smother attack if robust enough, Stealth bonus, fire vulnerability?

Stone:: +2 bonus to AC, dex penalty, speed penalty, some damage threshold?

Glass: Standard AC, make a rule for the broken glass?

Metal: Damage threshold, previously stated. 

Quote from Vaprak_The_Destroyer >>

Wood: Standard stats, some fire vulnerability depending on the type of wood

Cloth: Dex increase, acid resistance instead of immunity, climbing, smother attack if robust enough, Stealth bonus, fire vulnerability?

Stone:: +2 bonus to AC, dex penalty, speed penalty, some damage threshold?

Glass: Standard AC, make a rule for the broken glass?

Metal: Damage threshold, previously stated. 

 Excellent thoughts. I don't know why I hadn't considered speed changes or damage threshold. I'm updating my original post with some changes. Thanks!

Thank you!

I've added Paper Mimics and have decided to tie the AC of each mimic to the material it is trying to mimic. Thus a paper mimic only has an AC of 11 but a Metal Mimic has an AC of 17. I'd love any other thoughts anyone has for this idea. 

I actually kind of appreciate you bringing this up, it gave me something to do! Here is a thing you can do with the mimic: Have an exceptionally large one run thru the streets, causing havoc. Have fun with the stat block on it.

Octopi can mimic textures as well as colors and its not like the Mimic is trying to perfectly capture the thing that it is mimicking, its is merely trying to mimic something well enough to surprise its prey. I think the distinction should be much more about size then appearance of texture. I can see the distinction being made for the transparency of creatures as well, like with glass mimic.

As far as that is concerned, There are cases of biological transparency that allows for flexibility as well. Having it be weak to bludgeoning and break after taking a certain amount of damage seems strange for a biological creature. Perhaps treating it like plastic and making it weak to piercing damage? That way you don't have to worry about any special rules for broken glass.

The other stuff that you said seems really interesting tradeoffs for hyperspecialized mimics.

Check out this thread, it might have some helpful information.