This is one of the most memorable stages in the game, with an environment that feels icy and slimy, yet cool just the same.
From the start, you'll first head right over a series of ledges that span a bottomless pit. There are a few gaps between solid footing, and you'll want to time each jump carefully because of the enemies that swarm overhead. These flying robots look like giant eyes at the center of a diamond, and they drop walls of flame. Both flame and robots can knock you into a pit, so the best tactic is to equip the shadow blade and use it for protection as you press to the right. It also works well on the penguins that inhabit the area.
When you work right far enough, Proto Man will appear long enough to explode a cap that blocks a tunnel you need to access. Then, without a word, he'll leave the scene.
Drop through the newly-opened passage and veer left as you do so, if you'd like to collect a 1-up icon. When you reach the bottom of the screen, move to the right and you'll find a bunch of tadpoles trapped in bubbles. One shot from your arm cannon will burst a bubble and set its tadpole robot free, while a second shot can dispatch of the robot itself. Break the bubbles so that they form steps and allow you to access the item canister.
When you've gone as far right as you can, a new ladder will lead you up to another room of tadpoles you must clear in order to access yet another ladder, which in turn leads to another batch of the tadpoles. Through this third set of the tiny robots and their protective bubbles, you'll find a small gap. Slide through and drop down, then proceed to the right.
Now you get to face some penguin-shaped towers. They have cranks spinning overhead, and those cranks are the only vulnerable spots on the machines. However, you can't just repeatedly jump and shoot those, because the dragonfly robots are flying through the area. Be sure to avoid those, and also the tiny penguin robots that spew regularly from the base of the larger penguin towers. The miniature versions fall quickly to single shots from your arm cannon, and leave behind goodies with some frequency, so you can use them to refill your depleted life energy if desired.
Past the first penguin tower is a ledge, then a second one of the towers. Past that, you'll find a ladder that descends into an enemy-free room, where you can use the Rush Coil ability to grab a large energy pellet. With that done, drop down to the room below and find yourself at a stage checkpoint.
The checkpoint is placed quite fortunately, as the area ahead can be somewhat difficult. Wade out into the waist-deep water, then near the edge use the Rush Marine ability to turn Rush into a submarine. Push to the right, firing bullets like mad, until you hit the ledge where the energy tank is resting. With that collected, quickly move right until the next low ledge you find.
Once Mega Man lands on the ledge, the Rush Marine ability will be gone (the meter was likely all but depleted, anyway). Quickly hop right along the ledges, avoiding the dragonflies that swoop down from above. The puffer-fish robots are also dangerous, as they discharge missiles when directly below you. The blast when the missiles strike is enough to knock you off a given ledge, so it's important to keep moving.
When you progress far enough to the right, you'll be able to collect another energy tank from a ledge before climbing the ladder that leads to the area above. In this room, there are two of the robotic rabbits, so take them out carefully before climbing the ladder at the room's upper left corner.
This new ladder leads to a room where a giant robot is stomping about. Climb halfway up the ladder, then face right and fire a steady barrage of bullets from your arm cannon. Most will harmlessly deflect away, but enough will hit the robot to destroy it without you having to put Mega Man at risk.
When the robot is dead, climb up the ladder, run across the ledge, drop down, and pass through the gate that leads to the area robot master.
NEXT: Needle Man