Both Matt Ryan (John Constantine) and Jes Macallan (Ava Sharpe) have been confirmed as series regulars for season four.
The song which John Constantine is singing near the end, after getting out of the shower, is "White Rabbit" by Jefferson Airplane, which also played earlier in the episode.
Tom Wilson, who plays Hank Heywood, played Biff Tannen (and some of Biff's relatives) in the Back to the Future (1985) trilogy, which also contained time traveling elements. In the episode "Phone Home (2017)", Nate went undercover by washing a car and wearing sweats, like Biff does at the end of the first movie.
When the Legends go to Woodstock, a split screen effect is briefly used. This is a tribute to Woodstock (1970), which used this effect extensively.