Buffy The Vampire Slayer

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.

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 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: 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.