"Off-model", Daily Slimer #146

via Wikipedia:

Off-model is a cartoon character drawn out of par with the original source material or model sheets. Off-model drawings are the products of artists or by cartoonists wishing to parody another franchise but not wishing to incur a lawsuit or commit copyright infringement by actually drawing someone else's trademarked characters. They may also be the result of sloppy work, where the character has noticeable differences in appearance throughout different episodes.