Ounce you have 8 Spell Books in a specific Realm, or color, of magic your casting and research costs for those spells starts being reduced. Reduction increases by 10% for each book after 7.

This is why so many "11 Book Strategies" exist.

8 Books give a 10% reduction in Casting & Research cost
9 Books give a 20% reduction in Casting & Research cost
10 Books give a 30% reduction in Casting & Research cost
11 Books give a 40% reduction in Casting & Research cost
12 Books give a 50% reduction in Casting & Research cost
13 Books give a 60% reduction in Casting & Research cost

Note that you can only start the game with a maxium of 11 books and I believe the Max number of spell books COMBINED you can have is 13.

Also it should be noted that Sorcery, Nature & Chaos Realms have an additional little trick up their sleeves which is a "Mastery" Retort that can reduce Research & Casting cost of their spells by an additional 15%

Additionally the CONJURER retort can also reduce SUMMONING spells even farther by another 25%. It also reduces upkeep of the Fantastic, aka summoned, creatures by 25% (although not below 1).

Therefore it is possible to eventually be able to cast the most powerful summon creature spells, like SKY DRAKES, for FREE!!!

Sky Drake normally cost 1k mana to summon and 4.5k to research. But with 13 Sorcery Books, Sorcery Mastery and Conjurer they are free to learn and summon although they do still take 19 Mana a turn in upkeep keep in mind.

Of course you still need to earn the extra books haha so it's not so broken a strategy lol.

If you are interested in trying the above be sure to choose Conjurer & Mastery at the start as it's much easier to gain books than the specific retorts you need.

You may also be interested in the Channeler retort if you do a lot of in combat casting or are going to have Fantastic Creatures around as it reduces upkeep costs by 50% and also negates the extra mana required when casting away from your fortress.

Hey all I thought I would add on here the auto spell picks the computer chooses/gets right off based on the # of books. It can be really stupid and trade you one of it's Rare spells, like Nature's Gorgons, for a junky common if your smart.


Life: Heroism@2, Guardian Spirit@3, Holy Armor@4, Just Cause@5, Healing@6, Holy Weapon@7, Star Fires@8, Endurance@9, True Light @10. Resurrection, Unicorns & Angel@11

Death: Life Drain@2, Ghouls@3, Weakness@4, Dark Rituals@5, Black Sleep@6, Darkness@7, Terror@8, Skeletons@9, Mana Leak@10. Black Prayer, Black Channels & Wraiths@11

Chaos: Fire Bolt@2, Fire Elemental@3, Eldritch Weapon@4, Hell Hounds@5, Corruption@6, Warp Creature@7, Shatter@8, Wall of Fire@9, Disrupt@10. Lightning Bolt, Doom Bat & Efreet@11.

Nature: War Bears@2, Stone Skin@3, Sprites@4, Water Walking@5, Giant Strength@6, Web@7, Earth to Mud@8, Wall of Stone@9, Resist Elements@10. Change Terrain, Cockatrices and Gorgons@11

Sorcery: Nagas@2, Psionic Blast@3, Phantom Warriors@4, Floating Island@5, Confusion@6, Counter Magic@7, Word of Recall@8, Dispel Magic True@9, Resist Magic@10. Flight, Phantom Beast & Storm Giant@11.