Mosh Pit

You'll need to craft a Datura Bomb that affects an large area.
The following ingredients are needed:
- Impact Shell
- British Gunpowder
- Datura Powder

You can easily get the ingredients by opening bomb crafting stations that are scattered all over the city. Moreover, you should get a Cherry Bomb to lure multiple enemies. You can either craft it or buy it. Use the British Gunpowder to attract enemies from a larger radius. Head over to the Fatih Camii building (you can travel there by using the tunnel entrances) and climb the rooftop. In the courtyard are 8 guards. Throw Cherry Bombs until more guards come in. Then throw the Datura Bomb when they are standing close to each other.

Sometimes there are no guards in the Fatih Camii Courtyard. Then, head for the Topkapi Palace. There are always at least 16 Janissaries in those gardens. Climb on a roof in the center, throw a first Cherry Bomb to lure two squads together and then another one to bring the closer to the two others. When they're all in the same spot, just throw you Datura Bomb. That should do it.