Enter these codes in the pause menu while playing. A note about the skills/upgrades/soul cheat: If you use that, you won't be able to get the trophies associated with the skill upgrades. Use it at your own risk.
|All skills, upgrades, and one million souls||Up, Down, Left, Right, Down, Up, Down, Up
|Level skip||Left, Left, Left, Right, Down, Up, Down, Right