If a creature’s passive perception is always “on”, as suggested by JC in a sage advice segment on the official dragon talk podcast, what is the function of the detect legendary action option for ancient and adult dragons in the monster manual?
Blindsight could help the dragon in that an invisible creature would still need to hide behind cover to avoid being noticed by the dragon. Also, it can help the dragon avoid the -5 perception penalty for visual perception in dim light (if applicable).
If a creature’s passive perception is always “on”, as suggested by JC in a sage advice segment on the official dragon talk podcast, what is the function of the detect legendary action option for ancient and adult dragons in the monster manual?
So the dragon can try to find creatures who rolled Stealth higher than the dragon’s passive perception, exactly the same as the normal Search action.
What about that explanation and blindsight?
Seeing something isn't the same as noticing something. You may be distracted, misdirected, or just focused on something else.
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Blindsight could help the dragon in that an invisible creature would still need to hide behind cover to avoid being noticed by the dragon. Also, it can help the dragon avoid the -5 perception penalty for visual perception in dim light (if applicable).
"Not all those who wander are lost"
Blindsight also has a much shorter range than it's regular vision.