Ninja Gaiden IIEdit
Collecting these will increase the "Kill Score" Karma obtained in Story Mode. There are thirty small Skulls and one giant Skull. Each small Skull awards a 3% increase in Karma amounting to a 90% increase in Karma. The giant Skull awards 10% increase for a total 100%. Note that the giant Skull can only be obtained in the Xbox 360 version of Ninja Gaiden 2 after all previous thirty skulls are obtained.
Ninja Gaiden Sigma 2Edit
For every 10 Crystal Skulls collected a 10% discount on the prices at Muramasa's shops becomes available, for a total of a 30% discount. Does not seem to apply to Chapter Challenge mode. There is no giant crystal skull obtainable in this game.
Ninja Gaiden 3: Razor's EdgeEdit
Finding and activating one will begin a Test of Valor.
This eerie looking object is a legendary out-of-place artefact that has been around for centuries.
Should the player find all 30 skulls, an additional last Giant Crystal Skull one can be found on chapter 13 in NGII. Its description alludes to an increase in Karma.
A gigantic crystal skull from ancient legend. According to legend, this enormous skull belonged to a giant who walked the earth long ago. In these ancient times, the world knew no peace, and tribes fought each other to near extinction. None could see an end to this chain of suffering, until the giant appeared. He vowed to bear the sins of mankind upon his own soul, and offered himself as a sacrifice to the gods. His skull was then locked away in a room overflowing with human suffering. The legend ends with a warning, "He who possesses this skull must accept the fate of the giant as his own."
- It is rumored, but unconfirmed, that collecting the last giant skull will also increase aggressiveness / damage done by enemies, cause enemies to wear slightly different outfits, allow enemies to use new moves, and also cause yellow essence to increase in value.
- One Crystal Skull changed location from Ninja Gaiden II and Ninja Gaiden Sigma 2.
- Visual guide for the thirty small crystal skulls in Ninja Gaiden II found here at "http://wikicheats.gametrailers.com/Ninja_Gaiden_2_-_XB360/Crystal_Skulls".