I did up a little bit of venomous gunk for Venomancer's Venomous Gale during my free time, seeing as how the current Shadow Strike missile for it did not fit very well. See if you like it:
Also change the spell's casting animation to "attack". Venomancer opening his flaps to spew out poison completes the animation.
If you're looking to download the model, it is right here (1.9kb).
The testmap, as usual, can be found here.