What are the unusual weapons?

The update now allows certain cases to drop when completing contracts. The case drop system works VERY similar to Counter Strike: Global Offensive, you have a chance at obtaining a variety of new weapon skins. Skins that can come in 3 conditions, and have a rare chance at also coming with a stat trak(you'll have a little number on your gun showing your kills, it's basically a strangifier)

As for the UNUSUAL effects, these are the rarest of qualities. These modify your gun to have a particle effect applied to them, much like VALVE quality weapons. You have Isotope(a green hypnotic type of ring effect), COOL(Turns your gun ice/navy blue with some snow flakes falling and having a icy mist to it), HOT(which makes your gun RED HOT with a steam effect) and then Energy Orb(which makes your gun red and cloudy like the energy hole effects) - As of right now, none have been found, but my guess would be ANY weapon can have the effects on them. Much like UNUSUAL hats, there's a variety of effects for most hats, it wouldn't make sense to have them on stock only.

Most of this is just guesses but using my prior knowledge of how these things work out and how this update looks, I'd say that

1) It's probably only stock weapons, like the skins 2) There are probably different effects, and I'm 95% sure that one of them is shown on the update page. On the picture of the pixelly-skinned rocket launcher close up with the statclocker thingy, the end of the gun is flaming, sparking, and smoking. I believe that will be one of the effects.