Hi,

1. Resource Renewal
Tree stumps, after a long time, regenerate, becoming saplings then trees.

Wood can be burned in a goblin furnace and turned into diamonds. 20 trees makes 1 Diamond. Diamonds can be sold for 100 gold each.

Gold can be used to purchase or stone or iron at a rate of 1 gold to 5 resource. A late game, non-tome (always researchable) power allows mana to be converted into gold, stone or iron at a rate of 1 mana to 5 resource.

This gives two separate mechanisms for getting more resource late game.

2. Mana Income
Diamonds can be converted into mana at a rate of 100 per diamond.

You can summon goblin apprentices. After 3000 turns (a day and a night) a goblin apprentice becomes an initiate and can research in the library, giving extra mana income. 1 initiate gives mana at 50% the rate of the Keeper, so 4 initiates means that the Keeper has 300% mana income.

– Vordrak