- When in Rome overlaps with the second half of Dark Victory, which means the Gotham rogues are all united under Two-Face's banner at this point. Riddler's return to Gotham during April Fools' Day shows he's still allied with Harvey Dent and it also explains Nygma's easy access to Mr. Freeze's weaponry and Scarecrow being loaned out. While the Riddler's ultimate goal is to determine if Selina knows Batman's identity, Two-Face wouldn't have been able to pass up the chance to cause chaos among the Falcones' Italian allies.
- Why does exposure to fear toxin make the Riddler see the Joker, specifically? Several reasons. One, Riddler is a manipulator, and if there's one person who it's difficult to manipulate, it's the Joker - most of Batman's other enemies have some kind of predictable pattern to exploit, including Riddler himself, but Joker is usually fairly unpredictable. Two, Riddler has a need for attention, but if you've got the attention of the Joker, your life is perpetually at risk. Three, Riddler is arrogant in intellectual matters but a coward in physical confrontations, and while Batman is usually willing to keep it at that level and has a no-kill policy, the Joker wouldn't care about solving the riddles if they came head-to-head; he'd just hunt down Riddler and kill him, or use him as bait for Batman, or some other ridiculous thing. Four, everyone is afraid of Joker, but most of the heavy hitters in Batman's enemies list are able to protect themselves at least to a degree, while the Riddler doesn't exactly have a huge number of armed guards loyal only to him or the ability to pulverise a skull with one hand. Meaning the Joker is the number one threat to Riddler's continued existence and the Riddler is well aware of this.
Fridge / Catwoman: When in Rome