Serial Killer - Assassin's Creed: The Ezio Collection - ACB

Perform an Execution Streak of 10 Kills - 20

This is easiest done in the Animus Virtual Training Program, in the Combat Training with Long Kill Streak - this will give you 2 minutes to get the biggest execution streak you can. You can use which ever people you prefer; just remember you can block an attack by Holding Right Trigger and X, when an enemy is attacking you. If you come out of your streak, which can be done in a range of ways; including being hit, evading or being grabbed.

Those you need 10 Kills to get the achievement, a Serial Killer is someone who murders three or more people.

Hidden Blade