The Devil’s Crown

Legend has it that a group of sailors uncovered a buried treasure consisting
of seven gems, and split it with the intention of running off, before being
struck by a mysterious force which sinks the ship and kills them all. This
leaves a wreck underwater, with 7 gems to retrieve, replace in a golden crown,
and bring back to shore.

Before each of the jewels can be revealed, you must find ways to convert
various flashing objects into their real physical forms. After revealing the
flashing gems you must do the same to those.

The ship is made up of 40 screens, each with nasties to avoid, although a
pistol comes in handy to shoot these down. You have limited oxygen, but there
are vats of it on the ship, for some unclear reason.