The Man with the Umbrella - S1-E3
Continuity mistake: When people start dying during the dalgona game and people start getting eliminated from the floor of the control room, you can see one of the screens on the left showing a player licking the back of his cookie. People don't start doing this until they see Gi-hun come up with it, and he hasn't had that epiphany yet. (00:39:26)
The Man with the Umbrella - S1-E3
Continuity mistake: Toward the end of episode 3 when player 119 stabs a guard in the eye and takes his gun, he then shoots a second guard in the left arm and holds him hostage. However, after Player 119 sees his guard-hostage is a very young man and decides to kill himself, we see the Front Man walk up to the scene and in that moment the guard-no-longer-hostage has obviously been shot in the right arm. Noticing this made me realise the jungle gyms on either side of the scene got swapped. It's a mirrored image. (00:47:07 - 00:49:03)
The Man with the Umbrella - S1-E3
Continuity mistake: The umbrella shape on the wall changes in between scenes from wavy lines at the bottom to straight.