DOOM v1.1 Registered DEMO3
Released December 16, 1993. Perfect level for a demo, after all the tight dark corridors the open air of E3M6 feels like an infinite vista.
Cool stuff in this demo include the protracted plasma-caco battle, some nice chainsaw deaths and a demon collapsing in front of the player from an imp fireball.
Note also the red sky remaining firey and hellish while the invuln sphere turns everyone else in the world white. Modern sourceports regard this behavior as a "bug" and make the sky white too, but the original game clearly does it The Correct Way.
Demo captured from the original .exe using Dosbox 0.72.