Cave Story/Egg Corridor (redux)

The Spur
You wake up in the Mimiga Village Lake without Curley (note that if you beat Ironhead without taking damage, you get a secret, but useless item). Don't worry, you'll find her later, but for now, it's time to get the best weapon in the game. If you traded the Polar Star for the Snake or Mgun, you can skip this section, it doesn't apply to you. But if you waited and still have the star, then you're in luck.

First go into Arthur's house and if Booster is still alive, he'll give you the Booster 2.0, which is awesome, and also mandatory if you want to get the third ending. Go back outside and jump up high and find the cave you fell out of in the beginning of the game. You'll end up in the first cave. Now go see the gunsmith, who is awake this time. Talk to him, and he'll confiscate the Polar Star, but then he changes his mind and says you can have it back - after he's finished making it. Apparently, the Star is an unfinished weapon, and the finished version is Spur. This weapon is virtually mandatory if you want to beat Balos, so be sure to get it.

In addition, you can return to the Labyrinth and head to the Gaudi shop and collect the Whimsical Star. This small item will orbit you (when equipped) to inflict minor damage. This can be skipped if you intend to speedrun the game, however.

Also in the Labyrinth is the Arms Barrier, which you were not previously able to get if you have chosen not to trade weapons with curley (obviously, since you got the spur), AND if you were able to make the tough jump in the Labyrinth and avoid getting the 0.8 jetpack.

Once you collected the desired items, go back to Arthur's house, and teleport to the Egg Corridor.

Egg Corridor
You warp to the Corridor, and find that not all is as you left it. The place is in ruins, with rubble and cracked eggs (plus the half formed, dead dragons that were inside) everywhere. Most of the enemies are the same, but watch out for falling spikes, they hurt. Watch out for the dragon zombies, though. They have long-range fire breath which deals heavy damage. Chithulu's abode is now vacent, other than some crushers, so just go through the abode to continue. Keep on Keeping on until you get to the egg monitoring room. it's empty and has a tempting treasure chest in the middle. If you collect it, you get a 5 missile expansion and fight an optional boss, the sisters. After the fight, proceed towards Egg Chamber #00. But save first.

The Choice
This is where the game starts to branch. At this point, you see that Egg #00 has been successfully hatched by Kazuma, who shows up after you take a peek at the computer. After some depressing predictions about the doctor, he offers for you to escape with him on the dragon. If you say yes, you will get the first, and worst, ending. Don't do that. Say no, and he'll present you with the final hope: if the core is destroyed, the doctor's plans can be stopped. It is a very risky plan, but, then again, this is a video game. If the odds stack against you, you can just start at the last save point. Kazuma proceeds to open a hidden door to the right, and goes through. Follow him to the outer wall.