Conversation so far:
When did Riddler return to villainy?
In Tony Daniel's Life After Death“
What was Riddler's return like?
Riddler is rocked by a bomb detonation, the trauma re-awakening his psychosis. Cackling, rambling and insane, he terminates his contract with Oswald Cobblepot and disappears.
What did Riddler do in his return?
In Riddle Me This, the Riddler still acts as a private eye and teams with Batman to solve the murders of a mysterious sorcerer named Sebastian Rothschild.
What did Riddler and Enigma want with the list?
Riddler and Enigma escape, delivering the Jade Society member list to Gilda Dent.
What did Riddler do after that?
Riddler is paid but is more interested in another reward
Are there any other interesting aspects about this article?
This occurs in Pieces, where Gilda Dent reveals herself to her estranged husband Harvey Dent.
Did Riddler and Enigma work with any other villans?
Riddler and Enigma defeat Batman and reunite the Dents.

Question: Who was penguin?
Self-contained rewrite: Who was Penguin?