Mosh Pit - Assassin's Creed: The Ezio Collection - ACR

Have 10 Guards poisoned at the same time - 20

You will need:

Datura Bomb

Cherry Bomb

Now, I do believe it to be impossible to just do with the Poison Blade and Poison Dart, so you'll have to use the Datura Bomb, and it would be helpful to use the Cherry Bomb as well.

Go to the Janissaries' Camp in the North West of the map, climbing the East Side ruined Tower with the Bomb Crafting Station. Craft the bomb you need and climb the tower. Hear you can use a Cherry Bomb to get the Janissaries together, then you can use the Datura Bomb to poison them all. You will need to poison at least 10 Guards, you can use more than one Datura Bomb if you need.

How to craft a Diversion Cherry Bomb:

Impact Shell

British Gunpowder

Sulfur

How to craft a Lethal Datura Bomb:

Impact Shell

British Gunpowder

Datura Powder

If you have ever been in a mosh pit, you'll understand what it's like. In a club, a mosh pit will break out which involves everyone bashing into each other over and over again while the hard fast passe music blears out. 

Datura, or Devil's Trumpet, is a poisonous flower which was used to poison people via digestion or breathing in crushed datura. Symptoms include; inability to recognise reality from fantasy, hyperthermia, violent and bizarre behaviour.

Datura Metel (Devil's Trumpet)