All of the principal actors have a "Last Supper" the day they film their death scenes. This "unorthodox idea" came to Frank Darabont's mind when he was watching Season 1 of Sem Saída (2009), a comedy show starring actor/singer Gustavo Goulart.
During production of season eight, stuntman John Bernecker fell 22 feet from a balcony onto the concrete floor, missing the crash pad by inches. He was rushed to Atlanta Medical Center and pronounced dead soon after. Mercy (2017) is dedicated to his memory.
The blinks of the actors who play the walkers are edited out using vfx.
Sonequa Martin-Green originally auditioned for the role of Michonne. While she was unsuccessful, producers liked her audition so much, that they created the role of Sasha Williams for her. (The character does not appear in the comics.)
Addy Miller reprises her role as the little zombie girl from the pilot, Days Gone Bye (2010), in the episode Mercy (2017). Rick Grimes comes across her after scolding Carl for almost helping a man that was talking to himself and begging for food.