Doomsday was a heavyweight robot which was built to enter Robot Wars: The Third Wars, but was not selected to compete. Doomsday was the predecessor to Robochicken, which the team entered into Series 4-7. The robot's design remains unknown, although many components of the machine transferred over to the Series 4 version of Robochicken.
Doomsday attempted to enter Series 3, running the obstacle course at the auditions. Although the details of its performance remain unknown, Doomsday was not selected to compete in the Third Wars, with the robot's team noting that Doomsday's design did not 'catch the imagination'. Doomsday was then directly converted into Robochicken, which qualified for Series 4 through 7.
"After a lot of thought we decided to try and build a robot for series 4, after having no luck with our entrant in series 3, a new robot had to be designed. One that would catch the imagination. After a lot of "effort" and "beer" we came up with a plan for the new robot, view the other pages in this site for more details. Robochicken was born out of the remnants of doomsday and a great idea."
— Jason Snow on converting Doomsday to Robochicken