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).