Grimoire

Once a spellbook slot has a spell in it, that spell is locked for the duration of the run. Spells have to be purchased every run, there are no permanent spells.
The "waste management plan" at Waste suggests that spells can go in any slot, provided you have sufficient Dark Mana. Empirically, it seems that spells can only go into slots on the same double-page spread (TBC). If this is correct, then you can only use three of the five spells on each page in any given run.
There are 3 spots and 6 spells to unlock on each of the first three pages of the Spellbook.
Each spot in the spellbook can receive and one spell and spells cannot be used until they are placed in a spot. Once a spell is put in a spot it apparently can't be exchanged for another spell (TBC). The first three spots cost 100, 250 and 1e12 dark mana respectively.
There are 4 double-page spreads in the spellbook. The later pages have more powerful (and more expensive) spells. You can't turn the page to get at the later spells until all three spots on the first double-page are filled. Then you can scroll through and see what's coming up.
Once a spell is bought and moved from the left to the right page, it is stuck there for the rest of the current run, and only prestige clears the spellbook. (TBD Can some spells survive a reset ?)
====== Page 1 ======
Spell spots cost 100, 250, and 1e12 DM
*Summoning the Undead (13 DM) gives a Mana discount on Undead units
*Swamp Ritual (50 DM) generates 1 Mavka every 5 seconds for no resource cost
*Ark of the Drowned (145 DM) 100x waste product and 2x magic powder, when recycling raw mana in the Junkyard
*The Energy Circle (500 DM) 2x Energy regen and 3x crystal power
*Unholy Alliance (2e3 DM) Makes crystal #3 enhance Undead as well as Demons, and allows exchange of Hell Ashes and Bone Flour
*Red Flower (1e4 DM) 10x Demon productivity, and upgrades don't cost any Demons.
====== Page 2 ======
Spell spots cost TBC, 1e30 DM and 1e99 DM
* Equilibrium (2e20 DM) Using any crystal costs 1000 energy
* Aegis of the Plague (1e21 DM) Noted as DANGEROUS SPELL! Productivity of all undead units drops to ZERO. Every 2 seconds, 90% of your remaining souls are destroyed, BUT you get 1e12 Waste
* Animal Instinct (2e22 DM AND 666 Hell Ashes) Effect on Demons: Hell Ashes multiplier grows 666 times. Boilers can be blown up with any amount of Ash. 
* Empty Skull (5e25 DM) Number of undead does not decrease when upgrading. Adds Auto Upgrade to undead, every 2 seconds.
* Crimson Tear (1e40 DM) Cost of demons is decreased by 1000x This applies to all cost components, souls, gems and demons lower on the list
* Time Control (1e60 DM) Provides an additional menu that uses Energy
** 4000 energy Restore all Rotten Mushrooms to their normal state
** 2500 energy +1 hour to Mushroom growth
** 5000 energy +50% duration of crystals, capped at 100%
====== Page 3 ======
Spell spots cost 1e120 DM, 1e155 DM and 1e210 DM
* Candle (2e120 DM) Allows you to exchange Hell Ashes and Magic Powder, and gives you 100 Hell Ashes.
* Key to the Chest (1e130 DM) You will get a "Gift From The Chest" on any restart. Also, if you restart by opening the chest, you get 50% more prestige from Drowners (does this spell survive reset ? TBC)
* Warlock's Assistant (4e140 DM) 100,000x to each of Raw Mana, Dark Mana, and Crystal #5 power.
* Gossip (1e142 DM) Get twice as many resources when exchanging
* Break the Bond (1e160 DM) No more Raw Mana is needed to create Warlocks, but Souls are required instead. Warlocks do not get a discount on Souls.
* Ouroborous (1e222 DM) When you restart the game, the number of units is not reset. Cooldown of 42 hours.
====== Page 4 ======
The final spellbook page (so far) is different - there is only one spell spot which costs 1e300 DM to unlock
* Summon a Demon class Hero (1e350 DM)
* Summon a Warlock class Hero (1e650 DM)