The Demo lives off two weapons-the basic grenade launcher and the sticky bomb launcher.
How is that, you ask? Well, take a swig of the ol' grumpy bottle and have a listen. Indeed, until a fairly recent update the Demo was the one class that could be legitimately called overpowered. That said, I do pick up the bagpipes from time to time.
So this article should be taken with a grain of salt, as I am by no means a Demo expert. In the hands of a skilled player he can be the most powerful force in the game, but he and I just never meshed that well.