An image of the H.I.V.E. Mistress seen in Final Exam (2003) appears on Stone's milk carton, indicating she is missing; She is later in the crowd scene with Slade's butler Wintergreen in The Lost Episode (2005).
Bumblebee makes her first appearance in a blink-and-you'll-miss-it cameo during the seen in the lunch room.
When Beast Boy covers the robot Cyborg's mouth he takes the shape of a sea star. This is a reference to Starro - a giant starfish-like alien that controls others by "hugging" their face. Starro is primarily a foe of Green Lantern.
The Cyborg robot has three read-outs on its control: BOOYAH, ATTACK and OPTIONS.