Here is the full list of all 100 Spellbook Demonslayers achievements.
Level up Synthesis to level 4.
Reach level 50 with Eden.
Obtain 20 buffs at once.
Level up Thickening to level 4.
Level up this spell to level 10.
Level up Midnight Sigil to level 10.
Level up Star Scourge to level 10.
Level up Deathbound to level 4.
Level up Meltdown to level 10.
Level up Juggernaut to level 4.
Level up Blood Barrage to level 10.
Level up Blitzkrieg to level 10.
Level up Eyepopper to level 10.
Survive 20 minutes with 66 or more Malice.
Level up Inferno to level 10.
Level up Acid Breath to level 10.
Survive 20 minutes with 55 or more Malice.
Level up Fortification to level 4.
Reach level 100 with any Spellbook.
Level up Demon Feast to level 4.
Level up Fracture to level 4.
Level up Shrinkage to level 10.
Survive 20 minutes with 44 or more Malice.
Successfully complete any stage with 4 copies of the same spell at level 10.
Reach level 50 with Sly.
Survive 20 minutes with 33 or more Malice.
Gamble at Ibrahim's Emporium 4 times in a single run.
Level up Monsoon to level 10.
Level up Samsara to level 4.
Reach level 50 with Astrid.
Level up Timmy & Tommy to level 10.
Reach level 50 with Jeanne.
Survive 20 minutes with 22 or more Malice.
Level up Toxic Blizzard to level 10.
Achieve a Regeneration amount of 77 or higher.
Reach level 50 with Speare.
Level up Bloodletting to level 4.
Level up Flame Lance to level 10.
Level up Madame Death to level 10.
Level up Revengeance to level 4.
Reach level 80 with any Spellbook.
Survive 20 minutes with 13 or more Malice.
Level up Trailblazer to level 4.
Level up Shrine Maiden to level 4.
Reach level 50 with Tammy.
Level up Throne of Darkness to level 10.
Level up Airavata's Arrival to level 10.
Level up Bloodspark to level 10.
Level up Freezing Rain to level 10.
Level up Acrobatics to level 4.
Reach level 50 with Berry.
Level up Agni's Sigil to level 10.
Level up Mending to level 4.
Level up Indra's Sigil to level 10.
Level up Winter Sigil to level 10.
Level up Cataclysm Sigil to level 10.
Open 69 treasure chests.
Obtain 10 buffs at once.
Level up Brainpower to level 4.
Level up Frost Shear to level 10.
Level up Intensity to level 4.
Level up Skewer to level 4.
Activate a Revive.
Level up Lethality to level 4.
Level up Dark Moon to level 4.
Reach level 60 with any Spellbook.
Level up Cremation to level 4.
Survive 20 minutes with 7 or more Malice.
Level up Brutality to level 4.
Have 4 level 10 Spells at once.
Level up Ardor to level 10.
Level up Nightshade to level 4.
Reach level 50 with Wolfe.
Reach level 40 with any Spellbook.
Level up Clairvoyance to level 4.
Level up Reverberation to level 4.
Level up Fire of Sinai to level 10.
Play 3 runs.
Earn 13 or more Astral Flowers in a single run.
Level up Slipstream to level 4.
Obtain 5 buffs at once.
Survive for 13 minutes to begin the Slaughter.
Level up Shotgun to level 4.
Level up Deadly Aim to level 4.
Level up Overload to level 10.
Reach level 20 with any Spellbook.
Level up Spectre Shot to level 10.
Level up Thunderswarm to level 10.
Survive for 4 minutes.
Unlock Enigma
Survive 20 minutes with 77 Malice.
Reach level 125 with 77 Malice.
Reach level 125 with 77 Malice with every spellbook.
Reach level 125 with any Spellbook.
Reach level 50 with Vella.
Reach level 50 with Enigma.
Obtain 30 buffs at once.
Obtain 40 buffs at once.
Obtain 50 buffs at once.
Achieve a movement speed of 420% or higher.