8. Everything That Happened In Hush
There's a lot to recommend Jeph Loeb and Jim Lee's Hush storyline, but it's not perfect. We mean, what is? Amongst all the other shenanigans going on with dead sidekicks seemingly coming back to life, it's easy to forget that the Riddler went through his own massive changes during this Batman crossover, too.
For starters, it turned out that Nigma had been diagnosed with cancer,and that he was using one of Ra's al Ghul's resurrecting Lazarus Pits to try and cure himself of the disease. During his time in the pit he also figures out that Batman is Bruce Wayne - about seventy years after the rest of us, c'mon mate, catch up - and thus enacts the whole sordid plan that makes up the majority of Hush.
Teaming up with Dr Thomas Elliot, Bruce Wayne's childhood friend, Riddler sics Killer Croc, Poison Ivy, Harley Quinn, Joker, Clayface and Scarecrow on the Dark Knight. It doesn't work out, as these things tend not to, and the newly-rejuvenated but much more insane Riddler has to keep the revelation about his arch enemy's secret identity to himself, lest Ra's al Ghul and the League Of Assassins hunt him down for using a Lazarus Pit without asking. It's just impolite.
After things go sour for our villain, he gets beaten to a pulp by Elliot - aka the titular bandaged bad guy Hush - and is stripped of his deductive powers, left to live the rest of his existence as a member of Gotham's homeless population. Eventually he manages to get himself out of this mess, thanks to an ex-NSA employee and some extensive plastic surgery, but it was a weird time in the Riddler's life in general, and not one that seems to have affected any of his later appearances.