Enter these cheats on the [Pause] menu screen except the cheats marked with an asterisk, which should be entered in the [Title Menu] screen. Before entering them, be sure to set the control type to "Keyboard" in Control Options, otherwise they wont work. Note that for the U.S. version of the game you must have the v1.1 patch installed for these codes to work:
Disables Textures - Autoface, Down, TK Aim, Right, TK Aim, Up, Lift Attack, Autoface, Down.
Enables 'Wireframe' Mode - Autoface, Down, Autoface, Up, Feed, Autoface, Down, Lift Attack.
Enables Invincibility - Up, Down, Right, Down, Feed, TK Aim, Down, Lift Attack, Autoface.
Infinite Reaver Gauge - Down, Down, Up, Left, Feed, TK Aim, Down, Lift Attack, Telekinesis.
All Special Attacks Immediately Available - Right, Down, Up, Down, Down, Feed, Lift Attack, Telekinesis, Down.
Raises the Health Gauge & TK Meter to Full Capacity - Left, Left, Up, Up, Autoface, TK Aim, Telekinesis, Down, Lift Attack.
Replaces Kain's Soul Reaver with Cardboard Tube - Up, Down, Left, Right, TK Aim, Lift Attack, Down, Telekinesis.
Replenishes Health Gauge, TK Meter & Reaver Gauge - Left, Right, Left, Right, Feed, Autoface, Telekinesis, Lift Attack, Down.
Unlocks Every Piece of Bonus Material (*) - Down, Telekinesis, Up, Left, Right, Right, Lift Attack, Down, Right, Right.
Unlocks the Entire Dark Chronicle (*) - Feed, Down, TK Aim, Autoface, Right, TK Aim, Lift Attack, Down, Autoface.
Willow's "Vehiculum Furtus Maximo" Kain / Toon Raziel - Up, Down, Up, Down, Feed, TK Aim, Down, Telekinesis, Lift Attack.
Save the game after completing it to unlock all bonus materials.
Defeating stone statues
A bit into the game you will start to encounter stone statues that come to life and attack. An easy way to defeat them is to exit combat mode and run close to it. When it starts to attack, get out of range. It will hit the ground and be on its knees for a short time. Jump near it and press Y to do a mighty chop attack. The back of this creature tends to be its weak point. This will get more difficult depending on how many of them attack you at once. It seems that the most that will attack at once is three.
If there are more than one stone statue, try to get all of them close to each other. Go close to one of them and jump back when he tries to hit you. If done correctly, one of the other statues will hit the one that tried to hit you.
Defeating Janos Audron
Like Turel, he is invulnerable except for certain moments. Dodge him when he dive bombs you, then get in close and slash at him. You can also attack him after he has shot the orange tornado at you. Attack whenever he is down on his knees.
As Kain, use your combos and especially Kinetic Shackles. Pull or throw Raziel around and keep slashing. Raziel is quick; keep moving and use all your skills.
Finding the Earth Relic
When Kain is looking for the Earth Relic, hunt in whichever forge he is in. When you find a hallway filled with black Spectres (with purple eyes) run along it until you see a fence. Run in a half circle on the left side of the hallway. Jump over and down to find it.
Spirit Forge Puzzle
When you get to the Spirit Forge and the Elder God is closing it of with his tentacles, do the following. First, jump down and slash where the four connect. Next, climb out and use your Dark and Light Reavers in the holes on the ground (beneath the glowing runes). He will shout and drag the front deeper. Go down and slash. Use Earth Reaver to help get back up to the top. Do the same thing for Water and Fire. He will retreat deeper. Slash him again. Use Earth to sink and slash, Water to freeze the waterfall, and Earth to create to rock bridges. Climb to the top and stick the Air and Earth Reavers in to ignite the Forge. Then, just float down and get it.
Respawning Blood/Soul Basins
When playing as either Kain or Raziel, you will sometimes find Blood or Soul Basins which will recharge your health when you consume the contents. These respawn somewhere between two and five minutes apart from when you used them. This is very useful if you are locked in a room with multiple enemies, such as statues, which do not give either blood or souls upon their death.