XContra is a playable preview by Face Hugger released in 1994. It is based on the game Contra, which was known as Gryzor on the Amstrad CPC. The game itself was never finished.
The game features nice, colourful graphics and excellent sideways scrolling, although it is not possible to kill any of the monsters that appear on the screen.
- Screenshots
Mario is the guest star 
A nice large animated end-of-level monster 
A 'bug' in the last level!
Source Code
Source code from Face Hugger