Unlock Symphony of the Night
In Stage 2, while the minotaur is chasing Richter, immediately fall into the first hole in the ground, where you will be taken into the sewers. Play the level out normally and defeat the boss. Afterward, you will be taken to Stage 3' (the second Stage 3).
In Stage 3', whenever the path branches, taken the upper route. Make sure you obtain the Axe Sub-Weapon sometime during the stage. Eventually, you will meet a skeletal snake that is attached to a wall. Nearby is a vine-like cage, use the axe to cut it. It now serves as a platform for Richter to jump to the upper ledges. Continue along the upper ledges until you see a breakable tombstone. Inside is the item that unlocks Symphony of the Night. Return to the main menu to play it.
Unlock original version of Rondo of Blood
On your way through the end of Stage 4 you will find 6 skulls that spit fire stacked on top of each other. Just past them is a platform that moves like an inverted pendulum going left and right. Just opposite of it is a spiked ball. Get on the platform and jump over the spiked ball landing on the ground against the wall. Break the lower part of the wall to find a bomb. Hit the bomb to igite it, and the wall will come falling down.
Walk forward a bit and you will find 2 spiked platforms that try to crush you. Get on the right platform and as it's going up jump off of it and land on the upper level. Stay on top avoiding the axes and the yellow eye. At the very end of that platform is a candle, hit it and inside will be some classic gaming goodness.
Unlock Akoumajou Dracula Peke
The game "Peke" was introduced in the original Rondo of Blood as a bonus game if you used the wrong System Card.
First, you need to select NORMAL BOSS RUSH mode. Beat it two times, you will receive two Sound Discs. The third time fight until you defeat Shaft and defeat the next boss, at the end of the fight you should be rewarded with original game "Peke". Access it from the main screen like the other original games.
Boss Rush Normal
Beat the primary boss on each stage.
Boss Rush Dash
Beat the secondary boss on each stage.
Full Bosh Rush
Beat every boss, including Dracula.
Alternate Stage 5
Defeat Death in Stage 5, then go to Alternate Stage 4 and defeat Camilla.
Play as Maria in Rondo of Blood
In Stage 2, while the minotaur is chasing Richter, there is a candlestick that contains the Key Sub-Weapon. Make sure to get it, and proceed down into the sewers after the minotaur is blocked by the wall. At the very end of the sewer path, there is a locked door. Use the Key Sub-Weapon to unlock, giving you a cinematic scene where Maria joins Richter. She is now selectable as a playable character in the main menu.
Level Select for Rondo of Blood
Enter X-X!V''Q as player name.
On SOTN, Play as Alucard, with 99 luck and the Lapis lazuli (+20 luck) accessory
Enter X-X!V''Q as player name.
Completing the game first is not required.
Play as Alucard, with the Axe Lord Armor on Symphony of the Night
Enter AXEARMOR as player name after first completing the game.
Play as Maria Renard on SOTN
Enter MARIA as player name after first completing the game.
Play as Richter Belmont on SOTN
Enter RICHTER as player name after first completing the game.