The Riddler (Edward Nigma) is a fictional supervillain appearing in American comic books published by DC Comics, commonly as an adversary of the superhero Batman. The character made his first appearance in Detective Comics #140 (October, 1948) and was created by Bill Finger and Dick Sprang. Depicted as a Gotham City criminal mastermind, the Riddler takes delight in incorporating riddles and puzzles into his plots, and leaves them as clues for the authorities and Batman to solve. The character is one of Batman's most enduring enemies and belongs to the collective of adversaries that make up Batman's rogues gallery.
Return to villainy
In Tony Daniel's "Life After Death", Riddler appears early in the story at a gala party attended by Arkham, Dick Grayson, Huntress, and Oracle, hired by Penguin to find the Black Mask. As he chases Catgirl away from her robbery of the venue, the Riddler is rocked by a bomb detonation, the trauma re-awakening his psychosis. Cackling, rambling and insane, he terminates his contract with Cobblepot and disappears.  In "Riddle Me This", the Riddler still "acts" as private eye and teams with Batman to solve the murders of a mysterious sorcerer named Sebastian Rothschild (aka Sebastian Blackspell). Blackspell is apprehended, but only after Batman suspects Riddler went to great lengths to orchestrate the ordeal, including poisoning himself with a nearly lethal dose of Joker gas to skirt suspicion and act on a grudge between him and Blackspell.  Riddler's return to villainy is cemented in "Eye of the Beholder". Investigating the Sensei's attack on the Jade Society, Batman (Dick Grayson) is ambushed by Riddler and a young woman introduced as Enigma, Riddler's daughter. Riddler and Enigma escape, delivering the Jade Society member list to Gilda Dent. Riddler is paid, but is more interested in another reward, which Gilda promises after one more job. This occurs in "Pieces", where Gilda reveals herself to her estranged husband Harvey, who is now the disfigured criminal Two-Face. She hires Riddler and Enigma to help Two-Face best Mario Falcone and reclaim his coin. The plan works; Riddler and Enigma defeat Batman and reunite the Dents. The Riddler is rewarded with multiple dossiers of himself. When Enigma calls him a has-been, Riddler retorts with a new riddle: "What's green and purple and bleeds profusely?". Enigma's response is cut short by her scream, implying that the Riddler has murdered his own daughter.

Q: when did he return to villainy?
A: unknown

Q: what was his return like?
A: Riddler's return to villainy is cemented in "Eye of the Beholder".
what did he do in his return?
Riddler and Enigma escape, delivering the Jade Society member list to Gilda Dent.
Riddler and Enigma escape, delivering the Jade Society member list to Gilda Dent.