Baba Is You is a puzzle game. Baba moves tiles around his world that define how the world works. The text "Baba Is You" means you are controlling Baba. If that becomes "Wall Is You", suddenly you are controlling all of the walls.
lexikiq finishes the game in record time.
Due to how fast the levels are solved, the second set of encodes show them slowed down to 16.7% of the normal speed, with everything else at normal speed.
If you're interested in playing it, though, we strongly recommend you play it first before watching the TAS, as it evidently spoils the solutions to the puzzles.