You are about to reach the second ending, and make the choice whether to pursue the final and best ending.
After coming out from the last cave, you will have to face a few frenzied mimigas until you reach a shack where you can save and rest.
You can climb the cliff to the right to find a lot of powerups, health, and rockets.
Proceed all the way to the right to enter the throne room and begin some boss fights.
If you intend to go for the best ending, do not use your health potion for any of the following fights.
 Throne Room
Here you will have to fight Misery, after defeating her climb up on the newly appeared stairs. There you will face the doctor, when he is defeated, he will transform and have to be defeated again.
At this point you can pick up a few hearts by talking twice to the imprisoned Mimiga.
Finally, climb to the top and fight the undead core. strategy for fighting these bosses is available on the Enemies page.
After defeating those enemies you can either proceed to run all the way to the left and jump off of the island, triggering the second ending. Or you can enter the shack again, and start the hell difficulty ending in the Sacred Ground. Be warned that it is extremely difficult and will take a lot of trial and error to finish successfully.