Cave Story/Waterway

There really isn't much to say about the waterway; just a few things.

Spikes hurt
It's easy to let the currents send you into the spikes of pain, but if you're smart, you can make it.

Drain Curley
Curley needs draining after the incident with the core. Near the end of the artery, you'll come to an area where the currents are pulling you hard in all directions, but eventually, you'll get to a small exit near the top. This is where you need really good timing. There will be a slight overhang, jump when you are on top of it, and get to the oddly-placed cabin. You can save and restore health there, and if you have Curley with you, not going there will cause Curley to shut down permanently. If Curley is with you, look at the bookshelf, then take a rest. Curley will stay on the bed after you rest, so attempt to talk to her after checking the shelf to drain the water from her. Once that's done, save, then go back over to her and when prompted, say no, you don't want to leave her behind. You won't be able to come back here after you beat Ironhead, so you don't want to leave her here.

Ironhead
Ironhead is a pushover. Just get behind him and rapid fire at his back with super missiles. He'll be dead in no time.