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The Invisibility condition states:
For the purpose of Hiding, the creature is heavily obscured.
Rules for The Environment state:
A heavily obscured area—such as Darkness, opaque fog, or dense foliage—blocks vision entirely. A creature effectively suffers from the Blinded condition (see Conditions ) when trying to see something in that area.
The Blinded condition states:
A blinded creature can’t see and automatically fails any ability check that requires sight.
A group of 3 characters is under the effects of Great Invisibility and takes the Hide action. Within a minute later, a group of hostile npcs (who do not have any abilities above darkvision and hearing) enters the area. Do they automatically fail all perception checks (thereby granting the invisible party a surprise round)?