Age of Wonders: Planetfall (PC) - Achievement - Hide and Seek
Over the course of a single game, find at least 15 hidden Shakarn sleeper agents
This achievement requires use of the Shakarn Tactician. The hero ability to 'Call Insider' does not contribute to obtaining the achievement as it specifies they must be HIDDEN Shakarn sleeper agents. This means you must use the 'One of Us All Along' ability of the Tactician. You can use this ability on the same unit if you prefer until it dies, as long as it's an infantry unit. It can only be used once per battle though per Tactician and can only be used after 2 turns have passed in battle, so it's best to try and avoid damage until it's usable.