Buffy The Vampire Slayer

Slayer power:
Press Y(3), Black(3), Y, White, Black(2), White, Y at the extras screen. The sound of a scream will confirm correct code entry.
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Unlimited health:
Press Y, White, Black(2), White, Y Black(3), Y(3) at the extras screen. The sound of a scream will confirm correct code entry. Note: Falls are still harmful.

Multi-player arena 1:
Press Y(4), White, Black, Y(4), White, Black at the extras screen. The sound of a scream will confirm correct code entry.

Multi-player arenas 1 through 2:
Press Black(4), White, Y, Black(2), White, Y, White, Black at the extras screen. The sound of a scream will confirm correct code entry.

Multi-player arenas 1 through 3:
Press White(4), Black, Y, White(2), Y(2), White, Black at the extras screen. The sound of a scream will confirm correct code entry.

Multi-player arenas 1 through 4:
Press Y(2), White, Black(2), Y(5), White, Black at the extras screen. The sound of a scream will confirm correct code entry. All four multi-player arenas will be unlocked.
MrMexican22.

Play as Dark Buffy in arena mode:
Press Black, White, Y(2), Black(2), White, Black(2), White, Black(2), White, Black(3), White(2) at the extras screen. The sound of a scream will confirm correct code entry.

Multi-player story mode:
Enable the "Multi-player arenas" code. Select any arena, then exit out of it. Load a saved game and begin game play in story mode. Press Start on controller two when a major character is encountered during game play. If more than one major character is encountered in a scene, press Start to scroll through those that are controllable. Controller two can now be used to control that person. Press Back on controller two to stop controlling them. Note: You can also control Bosses.
Lucky_charm799.

Hint: Easy health:
When you start after a checkpoint and your life is low, intentionally kill yourself. When you resurrect, you will have double the life you had when you started at the checkpoint.
The Darkness.

Hint: Docks, Crane: Slayer training:
There is an area shortly after you enter where you are in the rafters, above a slew of vampires. Instead of taking them out with the crossbow, you can take them all on at once. Before you do this, make sure you get the Hellfire vial from the furnace on your right. Proceed across the rafters until you are directly above the gate that closes on you when approach it. Walk out on the rafter until you have a clear view of the gate, the crates (also below you), and the space between them. If you aim carefully, you can avoid the crates and fall directly in front of the gate. The damage taken from landing on the crates is easily fixed by an Elixir, or can be used as an extra challenge for those using the training. Land in front of the gate, and the intermission sequence closing the gate will start. You will take no damage from the fall. There are a total of six vampires down here (seven if you count the one that appears when you open the door). Take them all on at once for training.
Joshgotts12.

Hint: Dreamer Arena: Raise the pillar:
The Dreamer is not the only one that can raise the floor in the middle of the arena. Stand in the middle on the strange circle and press Y. Note: This was done in Arena mode.
Joshgotts12.

Hint: Spanish Mission - Courtyard: Elixir:
When inside the villa, climb up the haystacks to reach the top level. Then, break the wooden boards that are blocking the window near to where the key was located.

Hint: Sunnydale Cemetery - Entrance : Power Crystals:
Face the cemetery gate and search for a gravestone to the right. Break it to reveal a Power Crystal.

Drop down the hole created when the giant vampire appears to find a second Power Crystal.

Hint: Sunnydale Cemetery - Entrance: Elixir:
Get to the second courtyard and open the orange crypt door at the top of the stairs to find an Elixir.

Hint: Sunnydale Cemetery - Graveyard: Health Crystal:
Get towards the end of the level, where zombies spawn from tombs to attack you. A Health Crystal is hidden inside one of the tombs which are spawning the zombies.

Hint: Sunnydale Cemetery - Graveyard: Power Crystals:
Enter the main gate then immediately turn left. Break the wall behind two candles to find a Power Crystal.

Find the coffin the spawns the zombies. Search the small building to the right of the coffin to find another Power Crystal.

Hint: Sunnydale Docks: Holy Water:
In the room before the microwave and refrigerator is a huge box with a blue light shining on the wall around it. Attempt to break the box with your fists to get Holy Water.
stefan.

Hint: Sunnydale High School - Boiler Room: Elixirs:
Open the rusty door on the right side in the first room to find a hidden Elixir.

After the explosion, go back to the main staircase. Walk downstairs to the boiler room entrance. Open the janitor's door and move carefully behind the flames to find another Elixir.

Hint: Sunnydale High School - Gymnasium: Elixir:
Get to the corridor where the first demon dog appears. Walk up the stairs and enter the room next to the room where Willow was hiding in the previous level. Look bbehind the broken desk near the chalkboard to find an Elixir.

Hint: Sunnydale High School - Gymnasium: Holy Water:
After the intermission sequence with the man getting thrown through the doors, run through the now smashed open doors. Look for a brown locker in the hall. Open it to find a Holy Water.

Hint: Sunnydale High School - Library: Holy Water:
After killing the vampire that throws fire, enter the classroom. Look inside the small white wall compartment that is slightly open at the back of the room to find a Holy Water.

Hint: Sunnydale High School: Stakes:
There are a lot of vampires in this area. When you find the mop, use it and conserve it all the way down to a stake. The mop goes through many stages, spear then to stake. When you are out of the mop, the stakes will last for the rest of the level.
anyanka.

Hint: The Bronze Nightclub - Back Alley: Health Crystal:
Enter the doorway smashed through by the demon dog. Break the planks over the doorway inside. A Health Crystal can be found on the floor, near a corpse.

Hint: The Bronze Nightclub - Back Alley: Power Crystal:
Leave the room after the intermission sequence with Scylla. Jump on the barrel and climb to the platform above the entrance. Look behind the boxes to find a Power Crystal.

Hint: The Bronze Nightclub - Exterior: Elixirs:
Get all the way across the balcony in the spacious area where Spike is located. Jump down through the rooftop window to find an Elixir. Then open the big cupboard in this room to find a second Elixir.

Hint: The Bronze Nightclub - Exterior: Power Crystal:
Get to the glass roof, but do not drop through it. Use the pole to shimmy across to reach a hidden Power Crystal.

Hint: The Bronze Nightclub - Railroad: Elixir:
Use the cable to shimmy across from one rooftop to another. Break the four boxes behind a small wall to find an Elixir.

Hint: The Bronze Nightclub - Railroad: Power Crystal:
Search the left side of the far end of the railroad tracks to find a Power Crystal.

Hint: The Bronze Nightclub: Health Crystals:
Run upstairs past the giant vampire to the top level of the club. A Health Crystal is hidden under one of the wooden stools.

Go past the room where a victim flies through a window. Jump across the balcony to find another Health Crystal.

Hint: The Bronze Nightclub: Fighting Spike:
After you leave The Bronze and you meet Spike in the alley, you will not be able to defeat him. However, you can make it go quicker by pressing X, A, X while making Buffy turn in either direction at the same time. She will jump up and spin around while kicking Spike, which will knock him out. When he is on the floor, go over to him. Kick and punch him with a stake to lower his power level. A screen will appear and Spike will throw a fireball on the nearby gate. Make sure you do not enter the gate until all flames are extinguished. Then, climb on top of the tires and go up to the top of the building (not the trucks). A vampire will appear. After staking her, run down to the window and you will find another vampire. After staking him, run further down until you find the final vampire. After killing him, you can do two things: either jump down and go through the skylight into a secret room which has an Elixir; or walk carefully around the skylight until you reach a ledge. The game will stop and tell you that you have to shimmy across the pipe above in order to get to the other side to save Willow, and to also get another Health Crystal.
Nicole.

Hint: Defeating Evil Buffster:
Beat her up until her life is gone, then use the Hellfire Gun before you die.
Karitana.

To defeat Dark Buffy you must have Fire. If you do not, you must start from a checkpoint with Fire (three checkpoints back). Make sure over the course of playing the game that you have not put any Fire into your crossbow bolts before starting over, The crossbow will kill her instantly.
BUffsterB132.

Hint: Defeating The Master:
Use the giant spike frequently. It does three times the damage of your kicks. Eventually he will turn to dust on it.
anyanka.

Hint: Defeating Dark Buffy in arena mode:
First, make her lose all of her life. Then, she cannot move as fast. If you get completely out of her way, she will stop moving. Look around for a flame vial. Once found, hold R to aim then tap Y. Remember conserve your health for this. Also in arena mode, you can practice for your encounter with the master by completing arena mode 3. Once done the master appears, defeat him to claim your victory.
buffy burney.

Hint: Defeating The Master in arena mode:
The Master is fast, but Buffy is faster. First, use Hellfire. It is very good at weakening him. A few kicks and punches should allow you to take him down.
anyanka.

Hint: Defeating vampires:
Let the vampire rush at you and stake them when they are near.
James Seaniger.

Have your back facing the vampire, and when they are close stake them.
James Seaniger.

Knocking the vampire into the environment (for example, throw them onto a piece of wood sticking out).
James Seaniger.

Run towards the vampire, and when they are close, stake them.
James Seaniger.

The mutant vampire can be killed before you get the Reaper Blade. Treat him as you would any of the later vampires. You must get his health all the way down, knock him to the ground, and stake him. This is good training for anyone having trouble in the later levels, or for anyone who wants a challenge. Elixirs will help if you wish to use them. Note: This can be done multiple times in one run-through; even if you kill it, as soon as you leave it will show the vampire chasing you.
Joshgotts12.