Roy Harper wears his current comic counterpart's trademark hat for the first time.
Thanatos is the Greek word for death
The code for the box is 1013, which is stated to be the year the League of Assassins was founded and also Malcolm Merlyn's birthday (10/13). The number 1013 appeared frequently on The X-Files (1993) and 10/13 is creator Chris Carter's birthday.
The place where Oliver, Roy and Thea separated in this episode is the same place where Team Arrow and Roy was separated in season 3
At 28:00 Curtis mentions Alan J. Pakula who was an American director, writer and producer who was nominated for three Academy Awards.