Dive = Press "A" (Or B, whatever.) to become submerged beneath the water for nearly three seconds, becoming invulnerable to everything, more or less, but moving slightly slower.
The screen flag toggles it for the whole screen, whereas the quest rule toggles it for the whole quest. The screen flag simply reverses the current screen's ability to dive. I.e. if for one screen both are off or both are on, you'll be able to dive. If either one of them is on while the other is off for any given screen, you won't be able to dive. Think of it as a positive times a positive, a negative times a negative, a negative times a positive, or a positive times a negative. The first two are -yes- dive, the second two are -no- dive.
