The start of this level begins pretty slow, use this as some time to carefully re-level the weapons that got hit during the boss.
The real fun begins when you need to fight your way through the flowing currents to get where you need to go without hitting spikes.
You'll want to jump out to this small side shack if you're going for the Best End, as inside are some things needed to fix up Curly. If not though, continue floating on.
The water flow puzzles get pretty hard afterwards, and they climax at the end with…
Another boss, this quickly? Wait for him to charge forward and then float slowly back towards you. Unload all of your ammo into him as he floats back, and watch out for the smaller fish and debris.
You'll land back into the Mimiga village, which is not completely abandoned. Head down into Arthur's house and take the teleporter to the Egg Corridor. If you're going for the Best End and didn't get the Booster v0.8, you'll see Booster in Arthur's house and he'll give you the finished and better Booster v2.0!