At the main menu, select "Options", "Cheats", "Enter New Cheat", then enter one of the following codes to unlock the corresponding cheat option. If you entered the code correctly, a message will appear.

Always Slide - Press Green(2), Red(2), Yellow, Red, Yellow, Blue. This mode turns all guitar notes (not chords) into touch pad sliding notes connected by purple lines. It has no effect online.

Always Drum Fill - Press Red(3), Blue(2), Green(2), Yellow.

Auto Kick - Press Yellow, Green, Red, Blue(4), Red. This mode automatically plays the bass pedal for the drummer. It has no effect online.

Hyperguitar, Hyperbass, and Hyperdrums - Press Green, Blue, Red, Yellow(2), Red, Green(2).

Line 6 Effects - Press Green, Red, Yellow, Blue, Red, Yellow, Blue, Green to unlock additional Line 6 effects in the Music Studio.

Performance mode - Press Yellow(2), Blue, Red, Blue, Green, Red(2).

Metallica Costumes - Press Green, Red, Yellow, Blue(2), Yellow, Red, Green.

Invisible Rocker - Press Green, Red, Yellow(3), Blue(2), Green.

Air Instruments - Press Red(2), Blue, Yellow, Green(3), Yellow.

Black Highway - Press Yellow, Red, Green, Red, Green, Red(2), Blue.

Flame Color - Press Green, Red, Green, Blue, Red(2), Yellow, Blue.

Gem Color - Press Blue, Red(2), Green, Red, Green, Red, Yellow.

Star Color - Press Red(2), Yellow, Red, Blue, Red, Red, Blue.

Vocal Fireball - Press Red, Green(2), Yellow, Blue, Green, Yellow, Green.

Bonus characters - Successfully complete the indicated task in Career mode to unlock the corresponding character:

James Hetfield: Get 100 stars on vocals.
James Hetfield (Classic): Get 150 stars on vocals.
James Hetfield (Zombie): Get 200 stars on vocals.
King Diamond: Successfully complete the "Evil" song with any instrument.
Kirk Hammet: Get 100 stars on guitar.
Kirk Hammet (Classic): Get 150 stars on guitar.
Kirk Hammet (Zombie): Get 200 stars on guitar.
Lars Ulrich: Get 100 stars on drums.
Lars Ulrich (Classic): Get 150 stars on drums.
Lars Ulrich (Zombie): Get 200 stars on drums.
Lemmy: Successfully complete the "Ace Of Spades" song with any instrument.
Marcus Fretshreder: Get 55 stars on guitar.
Matty Can nz: Get 55 stars on drums.
Riki Lee: Get 55 stars on vocals.
Rob Trujillo: Get 100 stars on bass.
Rob Trujillo (Classic): Get 150 stars on bass.
Rob Trujillo (Zombie): Get 200 stars on bass.
Shirley Crowley: Get 55 stars on bass.
Zach Harmon: Get 100 stars in a band.
Zach Harmon (Classic): Get 150 stars in a band.
Zach Harmon (Zombie): Get 200 stars in a band.

Bonus instruments - Successfully complete the indicated task in Career mode to unlock the corresponding instrument:

Klown bass: Get 45 stars on bass.
Mean Green bass: Get 25 stars on bass.

Bonus songs - Successfully complete the indicated task in Career mode to unlock the corresponding song:

"Broken, Beat & Scarred": Successfully complete "The Thing That Should Not Be" song with any instrument.
"Cyanide": Successfully complete "The Thing That Should Not Be" song with any instrument.
"My Apocalypse": Successfully complete "The Thing That Should Not Be" song with any instrument.