Warning: spoilers ahead for the Season 4 midseason premiere of Gotham, called "Pieces of a Broken Mirror."
Gotham has finally returned to the airwaves after nearly three full months of hiatus, and the midseason premiere was a wild ride that introduced Ivy 3.0, reunited Jim with Lee in most unexpected circumstances, saw Butch regain his wits but keep his swamp body, and featured a toymaker/assassin. The episode may have also revealed which of the many Gotham rogues is the most dangerous at the moment, and it's not one that we might have guessed prior to this premiere. The most dangerous villain could very well be Ed Nygma.
On the one hand, Ed isn't exactly the most physically imposing character on Gotham. In fact, he was able to use his lack of general fighting prowess in "Pieces of a Broken Mirror" to convince Jim (who will soon have a very different look) that he wasn't up to anything sketchy. In a physical fight, Ed is probably one of the least frightening bad guys on Gotham. On the other hand, Ed has a well of brilliance inside of him, and he's currently losing his grip on reality in a truly dangerous way. He realized in "Pieces of a Broken Mirror" that he's been working in his Riddler persona without realizing it.
It took almost the entire episode for Ed to realize what he had done. For most of the hour, he was in full support mode as Lee's second-in-command while she began to rally the people of the Narrows to unite behind a good cause. When an explosive toy flew in and very nearly killed Lee, Ed was furious that somewhat tried to take her out and nervous about what might happen to her. His concern seemed genuine, and the fact that he could have been killed by the bomb that nearly killed her seemed to point toward him having no involvement in the incident.
The truth came out at the end of the episode when Ed was approached by the Toy Maker in the Narrows. Ed drew a gun and went after the Toy Maker, only to discover that he had hired the Toy Maker to take out Lee himself, paying cash and giving specific instructions about who to kill. According to the Toy Maker, Ed came to him in his Riddler persona and stated that Lee needed to die because she was holding him back. The only reason Lee survived was that Butch/Solomon Grundy managed to smack the explosive toy out of a window before it could reach its target.
Basically, Ed managed to almost kill a major character without actually knowing it, and that makes him even more dangerous than when he knew he was in previous seasons. It seems that trying to live on the up-and-up has made his Riddler alter ego even more ruthless, and that bodes badly for all the good guys in his sphere. We'll have to wait and see what happens.