Which Lego theme used augmented reality to interact with physical sets?

LEGO Hidden Side was the theme that used augmented reality to connect physical LEGO sets with digital play.

Launched in 2019, Hidden Side placed its stories in the fictional city of Newbury, where characters Jack Davids and Parker L. Jackson investigated supernatural events. Builders could use a smartphone or tablet app while viewing the physical models. The app added digital ghosts, challenges and interactive effects over the real set through augmented reality.

The theme was designed to make the physical model part of the game rather than merely a prop. Players changed or examined elements of buildings, vehicles and minifigures, then responded to what appeared on the device screen. LEGO described this combination of physical and digital interaction as “fluid play.”

Hidden Side is sometimes confused with LEGO Super Mario, which also combines physical construction with digital interaction, but Super Mario uses electronic figures and interactive components rather than the same AR ghost-hunting concept. Hidden Side was discontinued by the end of 2020 after 32 playsets and promotional packs.