Purchase at least one favor item. Use a text editor to edit the "Game.prefs" file in the "/My Documents/My Games/Gas Powered Games/Demigod" directory. Locate the "Items" section, and replace the existing values with the following to unlock all achievements and favor items.

Items = {
'AchievementVision',
'AchievementDeathReduction',
'AchievementXPIncome',
'AchievementGoldIncome',
'AchievementRunSpeed',
'AchievementPure',
'AchievementHealth',
'AchievementMana',
'AchievementPotion',
'AchievementTeleport',
'AchievementCooldown',
'AchievementAEMana',
'AchievementMovement',
'AchievementAERegen',
'AchievementManaLeech',
'AchievementSnare',
'AchievementDamage',
'AchievementRefreshCooldowns',
'AchievementFreeSpells',
'AchievementFlurry',
'AchievementFinger',
'AchievementMinionDamage',
'AchievementMinionHealth',
'AchievementMinionEvasion',
'AchievementMinionMeta',
'AchievementMinionBuff',
'AchievementAEHeal',
'AchievementMinionInvis'
},