The Stanley Parable's Narrator has taken over Portal 2. Real orders in his real voice, read from your own copy, and he keeps score.
You play Portal 2. Normally. The voice in the facility is just not GLaDOS any more.
It is The Stanley Parable's Narrator, in Kevan Brighting's own recorded voice, read straight out of your own installed copy of The Stanley Parable: Ultra Deluxe. He calls you Stanley. He tells you what to do. And he notices, every single time, whether you did it.
It hooks the campaign from the very first chamber, with his own opening narration, and follows you through the rest of it. Single player.
Portal 2, and The Stanley Parable: Ultra Deluxe installed on the same PC. Nothing of his is bundled here: the mod finds your Stanley Parable install itself and spends about fifteen seconds reading his voice, his subtitles and his music out of it the first time you press Play. If you do not own it, the mod loads and tells you so in Portal 2 rather than faking it with a soundalike.
Everything installs into portal2_dlc3, a folder Portal 2 mounts on top of its own content, so no game file is touched and deleting that folder removes the mod completely.
The Stanley Parable: Ultra Deluxe is by Crows Crows Crows and Galactic Cafe; the Narrator is written by Davey Wreden and performed by Kevan Brighting. Portal 2 is by Valve. Audio decoding by vgmstream.