Doomguy gets the portal gun. Open portals on any wall, fling demons through them, and let GLaDOS judge you.
Doomguy gets the Aperture Science Handheld Portal Device. Play DOOM and DOOM II's own maps with a portal gun on weapon slot 1, and GLaDOS watching.
What you can do
Really Portal, from your own copy When you press Play, the mashup reads Portal's portal-gun sounds, GLaDOS's real voice lines and her captions, and "Still Alive" from your own Portal install. GLaDOS welcomes you, comments when you start a level, die, find secrets, make big kills or fling yourself, and closes each level on the intermission screen while "Still Alive" plays. No Portal or DOOM files are included.
Good to know
Credits: made with Claude (AI). Runs on GZDoom. DOOM © id Software; Portal, GLaDOS's voice and "Still Alive" © Valve (song by Jonathan Coulton), all read from your own copies. Fan-made, not affiliated with id Software, Bethesda or Valve. Code and art: MIT licence; remixes welcome.