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.

Question: What did he do in his return?
Self-contained rewrite: What did Riddler do in his return?