When you finally get to Dr. Wily's castle in Mega Man 2, you get stymied by these floors that look solid, but you fall right through them. They're kind of tough to deal with until you remember that you have a (not so) secret weapon: the Bubble Lead.

The Bubble Lead follows the ground's contours (but never goes up, always down), so all you have to do is to fire one

and watch where it falls through the floor

Which makes it much easier to tell where the intangible blocks are, instead of trying to rely on your memory.