After reading a more recent thread, I had this idea Rocksteady should have done. Since there were various gangs in Arkham City, there could have been multiplayer.
The teams are Joker, Two-Face, Penguin, Tyger, Blackgate Prisoners and the Medical Team. Each team has a boss. The player to become the boss is selected at random. The player who kills the boss gets a bonus. The bosses are Joker, Two-Face, Penguin, Hugo Strange (Tyger), Aron Cash (Medical Team) and Ventriloquist/Scarface or Calendar Man (Blackgate Prisoners). Each boss carries an unique weapon which can be picked up if player kills boss.
Team Deathmatch - The team that gets the nessessary amount kills under the time limit wins the round.
Search and Destroy - Team deathmatch with no respawns.
Jammer - Team deathmatch but one team needs to destroy the enemy jammer and then activate their own jammer to be able to the end one round. The next round it is the enemy's turn to exactly that.
Free for all - Every man for himself.
Gun game - Guns cycle with every kill. First one to cycle through all guns wins.
Mano-o-mano - 1v1. Boss versus boss.
Alliance - 2v2. Two bosses versus two other bosses.
WW3 - 3v3. Three bosses versus three other bosses.
Extra - Kill The Bat! - First one to kill Batman becomes the Bat. Batman is fully upgraded which means you have be careful. The person to first kill Batman, becomes Batman immediately.
Extra - Kill The Cat! - First one to kill Catwoman becomes the Cat. Catwoman is fully upgraded which means you have be careful. The person to first kill Catwoman, becomes Catwoman immediately.
Every weapon available to the inmates in Arkham City, are available to the players. You can customize your weapons (assault/secondary) and lethal grenades. Once you level up, you can unlock armor and thermal vision gear (can be switched on and off, close proximity only) for extra gadgets. You can also customize the inmate you are playing as. Every level you play as for a specific team, you unlock new clothes, badges, etc. You can also customize the camo of your inmate's clothes and weapons. You can create your own emblem and title for your name.
You can also unlock perks, such as Punch (more powerful melee attack), Tech (carry two gadgets at the same time), Ammo (carry extra ammo for every weapon), Flash (run faster) and Stealth (no one can hear you).
I hope this interests everyone on the forum as well as Rocksteady, because this way people that like Shooters more than Action/Adventure game could get attracted to this. Thank you!