Eternal Darkness Cheats

Finish the game 2 times on the same save game to
get Level Select

Unlock Alternate Ending:
To earn the Alternate ending complete the game 3 times with a different
story each time.
Unlock Game Clear Bonuses:
Get the Credits option by defeating Eternal Darkness once. Defeat the game twice to have the option to play any of the chapters.
Invincibility:
Defeat the game a third time to be able to activate Invincibility for the
Chapter Select mode.

Successfully complete the game to unlock the "Credits" option.

At the beginning of Ellia's chapter, instead of going straight and examining the statue, immediately go into the right door. Going through that section of the temple first eliminates half of the trouble. Afterwards, continue as normal.