When Angel hands Gunn and Fred a drawing of the artifact that they are going after, Fred is surprised by how good the drawing is and of the later picture of Cordy. During Buffy the Vampire Slayer (1997), Angelus would leave drawings behind to scare the Scooby gang - several of Buffy, one of Jenny Calendar and in his own series, he drew Darla.
When Gwen fuses her client's watch, he cries, "That's a $12,000 watch," to which she coolly replies, "Now it's Surrealism." This is a reference to Salvador Dalí's famed painting "The Persistence of Memory," which depicts melted clocks and watches.
Alexa Davalos says she had "5 minutes of training" from stunt coordinator Mike Massa right before filming the fight scene with Angel.
Wesley references the Eleusinian Mysteries which is a cult or religious sect of Ancient Greece. Very little is known about the rites and practices of the cult other than the fact that they focused on the goddesses Demeter and her daughter Percephone, the latter of whom was abducted by Hades and made his bride. This is the only real connection with the mysteries and the underworld that were the basis for the Dinza character.
This is the only episode of the fourth season, and the last episode of the series, not to feature Andy Hallett as Lorne.
Angel mentions that he has done "a heist like this" twice before. This is possibly referring to The Shroud of Rahmon (2000), where he and Gunn infiltrated a group to steal the Shroud of Rahmon, and Choices (1999), where he and Buffy broke into the Mayor's office to steal the Box of Gavrok (In Angel's defence, both heists were successful, although the Shroud nearly drove everyone involved in the heist insane due to its nature while the Scooby Gang had to return the Box of Gavrok after the Mayor captured Willow).