At L20, in addition to getting their fun Black smoke wraith form, Defilers get an illusion that makes them look like a mysttail rat (the racoons with scorpion tails). If you cast it before you cast Wraith form, you can be a scorpion-racoon covered in black smoke. Useful in PvP if you want to keep a lower profile.
At L20, Furies get the ability to make themselves glow green. This can also be combined with lion form, and I imagine their AA forms.
Assassins do get a pet rat. Combine it with a rat totem, and you have a 2 rat army.
Illsuionists get 2 incredible illusions. They can be a bald human, or a bald half elf, which looks exactly like the human, but shorter. Perhaps you would think that an Illusionist, being master of Illusions and all that, would get fun, interesting, or cool illusions. Nope, we get to be bald humanoids. I think we get gnoll form at 35 (which anyone can get from a collection quest), and the ability to turn our whole group into bald humans at L40, I think.