Hey wait why only creature? What about artefacts? Some Artefacts could have an own will. They could wisper to you, control your body, or give you additional abilitys like nightvision as long as the like you.
A sword that actually possesses you when you go berserk in battle, replacing your mental attributes and skills with its own would be very, very interesting.
And that is the kind of magic sword I can support. Fireballs and "laser" shooting and "suddenly able to cut anything even though it's made of bone" - that is silly.
Substituting its will for yours... has some vile appeal to it.
... What if the person possesed dies? Will the artefact throw a tantrum?
Alcohol is also an Mitosis-poison (which i didnt see on the list yet) and manipulates the Enzyme processing of the cells. Mitosis-poisons slow down and stop normal growth which would explain an dwarves stature.
Dwarves drinking aeons ago and due to this evolving into booze-resistant creatures, that has being short as a side effect? Awesome.
I wonder if you could make creatures with poisonous skin... or poisonous meat; DON'T EAT THE GIANT FROGS, DWARVES! DON'T DO IT! NOOOO!
Perhaps it will be possible to create creatures like those. [Venon/Contact poisons] So if the outer skin layer is = given poison type, the skin of the creature should be poisonous. Well perhaps Toady could give us a proper answer, because I am just guessing. I am not sure that a poison can act like a skin layer at all. 
It would be QUITE neat if you kill it with, say, a sword and some of the poison forming a light covering on the sword. Like the blowdarts with frog poison.
