Castlevania: Dracula X/Stage 4

In order to access Stage 5' and save Annet, you must do the following:
 * Get the key from Stage 3 and keep it to the end.
 * Do not get killed ever once.
 * At area 4-4, save Maria by using the key on the door.
 * At area 4-6, use the key again on the door to skip the boss and go to Stage 5' (the door will not open if you did not save Maria, even if you still keep the key).

Secrets

 * 1-Up crystal: at the beginning of the area with the elevators, in the wall at the bottom-right.
 * Maria: use the key and open the door in the area with the elevators.
 * Passage to stage 5': use the key on the second door you see.
 * Roast: in the boss room, in the small platform under the candle on the right.

Boss: Minotaur
The minotaur is the easiest boss in the game, as you can manipulate his artificial intelligence so it never attacks. Simply run to the opposite side of the room and make sure he's as far away as possible. Approach him, and attack, then back away quickly. If he hops or moves backwards, go in for another attack. Keep your distance so he won't attack.

If you're close and above him, he'll throw rocks at you. If you are close to him and on the ground, he'll strike you with his axe (he'll also attack if you attack him a few times in a row).