Nemesis! is a custom campaign created by Bullway. It features 15 original levels with multiple paths. Several interesting and difficult creations ranging from space station obstacles to asteroid fields to massive mini boss enemies. You can find Nemesis in the CounterAttack Workshop.
Interested in creating your own custom level? Check out the in-game level editor by clicking "Garage" on the main menu and "Level Editor" in the Garage menu. If you have any questions related to custom levels, campaigns, or the workshop in general feel free to post in the CounterAttack workshop discussion forum.