Why restrict ourselves to tilesets? Some of these I'm more confident about than others, but let's get started:


Tweedledum and Tweedledee from the Disney movie Alice in Wonderland
This is pretty straightforward. The original illustrations were uncolored, and the book's text only describes them as fat, but the JJ2 sprites copy the movie's blue bowtie, orange hair, and red pants, although in JJ2 they're suspenders. The hats are sort of a combination of the movie and the illustration, but modified to be a propeller beanie.


The Mad Hatter from the Disney movie Alice in Wonderland
While we're on the subject. Again the movie's version is similar to the original, but the movie and the JJ2 sprite have much more dramatic hair, and the book version's top hat doesn't have a colored stripe around it.


Sebastian from the Disney movie The Little Mermaid
That tall face is pretty distinctive. I don't know if Sebastian ever uses the crab enemy's distinctive claws-in-the-air-like-he-doesn't-care gait in the movie, but he doesn't in the Little Mermaid game on the Genesis.


Evinude from the Disney movie The Rescuers Down Under
The colors are different, probably to make it easier to see in naturey tilesets. The giveaway here is the big cartoony eyes and bushy mustache.


The Ghostly Trio from Casper the Friendly Ghost
Maybe? They have legs, which is a big difference, but the chubby cheeks are suspicious.


The kitten from the Looney Tunes cartoon Kit for Cat
This may be a reach, because there are only so many different cat breeds.


Turtle Goon enemy from Jazz Jackrabbit 1
Not quite copied and pasted, because they use different shading and a few other edits, but the silhouettes are almost identical. The JJ2 version has twice as many frames, though, to animate more smoothly.

Crow enemy from Earthworm Jim
The shape of the beak and the expression have a strong likeness.



Marvin the Martian from Looney Tunes
While the coloration on the helmet is different, because of how it obscures the face sans the eyes, it's likely that Marvin was an inspiration for the design of the Helmut enemy.



Pinky from Pinky and the Brain
Pinky is much more goofy, but there are similarities in the body shape, coloration of the body and limbs and both have a red bobble nose (but much less pronounced in the case of the Lab Rat enemy).