A ten-level solo scenario, and a net level (Lava Extreme, also available separately) Some of the levels are bigger than others, but except for the last one, you can run through the whole thing in under an hour. The story revolves around Durandal and Tycho, but they're not the Durandal and Tycho you know... Use IZD on an 040. (The last level shows what happens when you give someone All Roads Lead to Sol and DOPE and tell them, "make a level kind of like this one, but with more monsters.")
A simple net level, probably best with two players. A couple of ledges are separated by a lava pit. One player can control the lava, and teleporters from one side to the other are at the bottom... just make sure your opponent's nowhere near the switch when you jump in.