Devil's Sea (aka 'Treacherous Waters') is unlocked once you reach the Master * Rank. So the earliest you can access it is after rescuing Scizor.
It is in the Miracle Sea, on the 18th floor
bottomless sea
no
Enclosed Sea, Miracle Sea, Bottomless Sea.
yes, in miracle sea or surrounded sea.
Boner
50 in Pokemon mystery dungeon explorers of time
20 floors
Bottomless Sea has 50 floors.
Qwilfish can be found at Bottomless Sea.
if you mean on the dungeons list AEGIS CAVE is after miracle sea..veronica
miracal sea 3F if ur holding a mystery psrt or secret slab