Here's a fairly recent Knuckles, from around 2003. This is by Sega Toys...but as you can see here it's got some errors. First off is he's missing the yellow part of his shoes. This makes his feet look pretty strange, so it's really odd that something like that would slip by, especially since it's "Sega Toys" and not some (nefarious) 3rd party like ToyNetwork. The other error you can see is...he has FINGERS. Yes, they've actually gone to the trouble of putting a detail that's not even supposed to be there.

However, otherwise it's a decent plush. Good proportions all around for the most-part, decent expression, and just fine fabric.

This Knuckles and the Tails below both share sort of 3D-ish plastic eyes. The 'bead-like' things they used have a bit of depth, which you can see with the Tails. Both photos by Memeki.
***Apparently someone still has a few of these in stock, if you want them! You can go to the CMD Store and order these two. (they're a bit pricy since they're from 2003) but watch out, as there are also the nasty ToyNetwork plushes on the same page. Selling in Jun.2008*** (link will be removed when store runs out)

In a further look at this plush, you'd expect it to be from a "Sonic X" collection, but it had no Sonic X tag, and the eyes are purple rather than a dark blue. Also, the fabric is softer with a fuzz rather than the smoother/tougher fabric on the usual X plushes. Also note the non-drooping/wilting tail and the curving not-loose head spikes. This is an interesting and different plush, when you really inspect the details.