Gotham Knights

With the Heroic Assault and Showdown Title Update, you can grind the Talonted achievement on the way to getting this one:
Floors above 20 have Talon enemies. In particular Floor 28 has Hunter Talons, which are likely the last of the three types you will need to unlock this achievement.

The achievement will unlock in Heroic Assault mode (myself and a friend both got it), and your kills in the NG/NG+ will count toward the totals needed here.

If you have completed the main story, and progressed in New Game + enough to reach 7.1 in the main story again, all 3 types of Talons should now be available to you.

It is quite likely you already have the 40 feral Talon kills, as they are the most common kind. So you’ll just need to focus on the Gladiator Talons (big guys with shields and maces) and the Hunter Talons (look similar to Feral Talons but dual wield knives).

The best activities you can do to fight these enemies are the Owl’s Nest clean out missions. Unfortunately you won’t get more than one a night if you’re collecting all your clues; however, I found a simple way to hunt down my remaining Talon kills.

Each district of the city when you enter to start your patrol for the night tells you which factions have a presence there that night. The Court of Owls symbol is what you’re looking for. Even if you haven’t uncovered an Owl premeditated crime, you can still track down Talon crimes by scanning the map and looking for districts that show the Owl symbol under factions in that district; fast travel there, then do a little patrol. Undiscovered premeditated crimes will show a ? Triangle symbol when you get remotely nearby. Hover over it on your map to see if it’s an Owl mission and go complete it if it is.
If it’s not, then start visiting your opportunity crimes in the district, and look for Talons or Owl guards at those. Some are simple crimes with a Talon or three in attendance, others may be seemingly “completed” crimes with chests to open, one of which is a trapped chest that summons the Talons to ambush you.

Simply rinse and repeat these by completing them until the district no longer shows an Owl presence, then return to the Belfry and start a new night.

After completing the game and then nearly all of New Game +’s story (stopped just after unlocking the Man-Bats to finish that achievement), I only needed about three nights worth of this to finish this achievement.

The different types of enemies with the Court of Owls appear as you progress the main story. Feral talons are the first to show up, Gladiator talons show up after mission 5.2 of the main story. Hunter Talons are the last and won't appear until 6.2. To find them in opportunistic crimes and court of owl missions, you should be at least on mission 7.1. This is also true even in the New Game+ mode.