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.

Question: What did they want with the list?
Self-contained rewrite: What did Riddler and Enigma want with the list?