Game has multiple difficulty levels. You can play in easy, normal, hard or legendary mode. In easy mode creatures are less dangerous, but your level and skill cap is quite low. You can finish the game but you will not see many items or spells game has to offer. Normal difficulty is what we expect most of the players will use. Hard is for hardcore players only. Legendary is for masochists. Monsters are twice as dangerous, they respawn quicker, they are more aggressive, attack in hordes, items are more expensive and merchants are trying to rip you off with their prices. However maximum player level, maximum skill level, maximum spell and crafting levels are almost 50% higher than usual, chests and other itemholders contain more items and you can find and craft hundreds of new items (mostly magical items) not available in easy and normal gameplay modes.
Each difficulty level has different limits regarding max level cap, max skill levels, number of craftable items, number of items per itemholder, monster strength and so on. We thought about it and decided to test the following idea. Instead of changing existing difficulty levels and rules, we implemented fifth difficulty level - Custom.
Custom difficulty level allows you to configure various parameters before the game starts. This way you can configure game to run in easy mode but with all items enabled, or you can start the game in legendary mode but with lowered monster health, or any combination of 8 basic difficulty parameters you would like. Lead programmer had to throw quite a few special programming spells to the code to make it work without endangering the balance.