In Blaster Master's Area 5 you come across a boss that is not susceptible to the pause trick, a giant crab.

Making things tougher is that this crab shoots out a ludicrous amount of bubbles that keep you from pelting its weak spot (its face) with grenades and have a side effect of killing you pretty quickly.

So what I do is exit and reenter the corridor leading up to the boss over and over again picking up gun powerups from the square enemies that litter the area. It's kind of tough since, if you get hit, you lose some of your gun power. Once your gun is fully charged, it's pretty unstoppable.

Then you can go ahead and enter the boss's room and hold down the A button (your grenade button) while wailing away on the B button (your gun button). Holding down the grenade button will ensure that you keep facing the same direction while you move back and forth, allowing you to keep up the pressure.

Eventually the crab will explode somehow and the Dive attachment will be yours!

Which will make maneuvering underwater so much easier.