Skullduggery is an achievement in Halo 4. It is awarded for completing any Campaign level with three or more Skulls activated on Heroic or harder. The achievement is worth 15 Gamerpoints. It is represented by a skull stacked on top of two skulls.
The achievement most easily achieved by playing through the level Dawn, which in comparison to later levels is relatively short and features fewer heavily-armed enemies.
The requirements of this achievement is exactly the same as "Tsantsa" from Halo: Combat Evolved Anniversary. This means that any skulls, including the far less difficult Cowbell, Grunt Birthday Party, and IWHBYD skulls may be used.