Stasis wards are cloaked traps added in Legacy of the Void to replace the oracle's envison ability. When triggered, they hit in a small area, freezing enemy units for 21 seconds. When trapped, these units cannot be attacked, but cannot be effected by allies abilities either. 
This unit is permanently cloaked. They cannot be seen or directly attacked by enemy forces, unless they have detector support.
Traps nearby enemies in stasis for 21 seconds. Trapped units cannot be attacked or affected by abilities.