Serious Sam 2 is a 2005 first-person shooter video game by Croteam. It was released for PC and Xbox.
Duke Nukem cameo
Duke Nukem has a cameo appearance in Serious Sam 2. In the swamp, a skeleton can be found hanging from a tree with a platinum-blond wig, sunglasses, and a small rocket in its pelvic bone. Upon discovering it, Sam will say, "Dude, you've been hanging here, like, forever," referencing the infamously long development schedule of Duke Nukem Forever. At the time when Serious Sam 2 was published, Duke Nukem Forever had already been in development for eight years, yet it still would not be completed for another six years.
Serious Sam cameo in 20th Anniversary World Tour
Serious Sam later made a cameo appearance in Duke Nukem 3D: 20th Anniversary World Tour. On the level Mirage Barrage, the corpse of Serious Sam can be found in a secret area beside the smallest pyramid. Upon discovering the corpse, Duke will say, "Why so serious... Sam?"