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