User blog comment:Gingergreeney/ARKHAM 3/@comment-5330380-20120826084915

There are many factors that allude to a sequel to Arkham City.
 * Harley's positive Pregnancy Test, though this seems to be a red herring since in Harley Quinn's Revenge we see several other pregnancy test and all are shown as negative. It could be that the baby was a stillbirth or the previous reading was simply false. It is also possible, given the relationship between the two, that Joker faked the Pregnancy Test to make Harley believe she was pregnant.
 * At the end of the credits, Harley can be heard singing to her baby, promising that she will kill "the whole damn world".
 * Batman commenting he will go after Hush tomorrow.
 * Hush is shown to escape Arkham City after altering his face to look like Bruce Wayne's.
 * Canisters of Scarecrow's fear gas in Hush's hideout.
 * Two-Face winning the gang war in the wake of Joker's death and Penguin's imprisonment, thus gaining control of the criminal underworld.
 * Azrael comments that Batman after saving Arkham City events would be set in motion that would lead to the possible down fall of Gotham & Batman himself. Azrael then promises Batman that they would meet again.
 * There are Scarecrow thugs carrying out Crane's bidding during the Protocol 10 Sequence all over Amusement Miles.[3]
 * The strange communications on the Cryptographic Sequencer, translating into I WILL RETURN BATMAN, YOU WILL PAY FOR WHAT YOU HAVE DONE TO ME, FEAR WILL TEAR GOTHAM CITY TO SHREDS. The last of which can only be decoded once you enter the passcode, SCARECROW.
 * Falcone's shipment to Scarecrow seen on Scarecrow's boat.
 * During the game's finale, when the Lazarus Pit is exploding, Batman is knocked unconscious with the cure in his left hand. When we wakes up it is in his right hand. Possibly meaning someone took or switched it while he was unconscious (It is possible this is the result of a continuity error).
 * Scarecrow's Fear Gas tanks can also be found in the city. [4]
 * Calendar Man's escape from his cell.
 * If the player goes to Calendar Man's cell as Catwoman, the two will engage in a brief conversation in which Calendar Man hints that Catwoman might be expecting something from her father & that it may involve the Falcone's. This may indicate that the next game may be based off The Long Halloween, in which Catwoman belives that that she is the daughter of Carmine Falcone.
 * Poison Ivy stating to Catwoman that she will have revenge on humanity.
 * Scarface disappearing from his display case, presumably taken by the Ventriloquist.
 * Bane vows to kill both Batman and Catwoman.
 * Deadshot vowing revenge on Batman for stopping him.
 * Ra's al Ghul's body disappearing from on top of the gate into the city, whilst his sword remains at the end of the game.
 * Talia's body vanishes during Batman's battle with Clayface.
 * Abramovici Twins teaming up.
 * Prometheus's record is found in the GCPD, passing the Arkham exams, as well as newspaper articles telling of two criminals gunned down in front of their son by police.
 * Peyton Riley is revealed to be the active Ventriloquist.
 * In Harley Quinn's Revenge Several Posters of Cadmus can be seen in Harley's secret base, all of which are located right next to a Joker model, possible hinting that Cadmus could be involved in the character returning.
 * When Robin enters the secret base for the first time Vicky Vale can be heard on the radio asking Gordon where the Joker's body is. Whether this means that the Clown Prince of Crime's body was stolen or if this is just meant to be a Red Herring is still unknown at this time.
 * In Harley Quinn's Revenge, Gordon tells Batman that after they've stopped Harley they need to deal with another problem.