oh, another thing that I should have added before making this page, but each of these will be using the "holotype" for that specific design. If you don't know, in paleontology and biology, a holotype is essentially the ideal specimin of a specific genus. In this context, that means I'll be using either the first image of a specific design, or the one that I think illustrates it the best.
So, I have found at least four major verions of Friend:
To give examples for each of these, I will use the eirliest known inamge for each design. Unfortunatley, it's a bit tough finding the original version of each design. If you know who created the original versions of some of these designs, send an email to freedominthe@usa.com. Now anyway, the primary difference between each variation is the face. Namely, the eyes, eyebrows, and mouth.
This one is probably the most simple out of all of them, as it is pretty much just a greyscale Woody, with some slight artifacting. Later fanmade versions depict Friend Inside Me as being far more elaborate.
The version of Friend inside me that is probably the most common (it's even the first google search result for "Friend Inside Me") The main difference here is the much heavier JPEG artifacting that has caused his pupils to go entirely dark. This is the first consistant difference that we'll see from now on.
Another very common variation of Friend. Can be found in the Deltarune: Friend Inside Me mod, and as the name would imply, the animations by atticted. Typically, the atticted Friend lacks eyebrows and carries over the all-black pupils. On top of that, this version is commonly seen without a hat.
Now, according to some insider sources, this one was pioneered by the former Twitter user @FriendInsideMe0, hence the name. (AKA the "EXE" design, Called so for its more "traditionally spooky" look.) This version is strikingly similar to the standard Fanon Friend, but lacks teeth and often has a much higher color contrast. This variant is arguably the most widley-used variant, being the basis for some iconic Friend Inside Me images (including the HD Friend Inside Me renders made by Reddit user U/Inevitable-Fig9808.