During Harv Hickman's party, one of the guests is wearing a hat/helmet believed by some to be modeled after that of DC Comics' rival Marvel Comics' space-fairing character Galactus. However, this is actually Devilance the Pursuer. Both characters were designed by Jack Kirby and he was known for reusing designs on other characters.
The guest at Harv's party dressed as Batman is doing the "Bat-tusi", a dance popularized by Adam West in the 1960's live action series.
When the Flash calls the worm monster "Cecil" he's making a reference to a kids cartoon character "Cecil the Sea Sick Sea Serpent" created by Bob Clampett.
At Harv Hickman's costume party there are several guests dressed as DC Comics characters. Those include: Dr. Bedlam, Black Racer, Vykin the Black, Goody Rickels (a parody of Don Rickles), OMAC faceless agents, Harley Quinn, and Devilance the Pursuer.
A number of the characters mentioned at Harv's party were created by famous comics artist/writer, Jack "King" Kirby - who also created Jason Blood / Etrigan and (this version of) Morgaine le Fey for DC Comics.