Donna mentions Roy Harper, who was the original Speedy in the comics, sidekick to Green Arrow and a member of the original Teen Titans along with Donna and Dick. Much like Dick he eventually outgrew his sidekick role and took on several other hero identities, most notably Red Arrow and Arsenal. He has previously appeared in the CW series Arrow, portrayed by Colton Haynes.
The code to open the door at Slade's house, 5639, spells JOEY - possibly referring to Slade's son Joseph, who was known as Jericho in the comics and was a member of the Teen Titans.
The first appearance of Rose Wilson (Ravager), Arthur Light (Dr. Light), Selinda (Shimmer), & Faddei.