Act 2 is a return to underwater sections, but with the added complexity of industrial machinery. You'll encounter strong currents, crushing blocks, and electric barriers, all while managing your breath. The Bomb Badniks are prevalent here; they fly around and drop bombs, so be careful when navigating underwater. Look for air bubbles diligently, as they are often scarce.
This Act features a long, winding underwater maze with numerous dead ends and hidden paths. You'll need to activate switches to open gates and progress. There's another 1-Up Monitor: after a long underwater section with strong currents and crushing blocks, you'll reach a platform. Instead of going right, look for a small hidden passage to the left, which leads to the extra life. This Act is arguably the most challenging in the game, combining the difficulty of Labyrinth Zone with the hazards of Scrap Brain. Patience and careful exploration are key.