In the part I remember, Pinky & the Brain showed up. I didn't get a good look at Pinky, but I unfortunately did for Brain. For those who know your Lovecraft? Brown Jenkins. For those who don't know your Lovecraft, imagine the creations in Island of Dr.Moreau, but critters with human bits instead of humans with critter bits. If you're into pictures:
(image from http://loneanimator.blogspot.com/2009/05/brown-jenkin-comes-alive.html)
...but with a face of a later-year Orson Welles (thank you, Maurice LeMarche).