Here is the full list of all 36 Secrets of Magic: The Book of Spells achievements.
Get 300 stars
Complete the Venom Antidote Spell
Finish all the levels in Challenge mode
Complete the Spell of Awakening
Complete the Spell to Remove a Werewolf’s Curse
Collect 500 spell ingredients
Get 200 stars
Complete the Spell to Hear Secret Thoughts
Use the Torch power-up on at least 25 spiders
Complete the Spell of Invisibility
Upgrade twice the Wand power-up
Complete the Spell of Truth
Make a combo of 25x or higher
Upgrade twice the Lightning power-up
Destroy at least 600 wooden gates
Play 50 levels
Complete the Spell of Healing
Upgrade twice the Whirlwind power-up
Complete the Spell to Fly a Broom
Destroy at least 245 spider webs
Upgrade twice the Stake power-up
Upgrade twice the Hammer power-up
Complete the Spell of Time
Destroy at least 130 stones
Complete the Spell for Invoking the Power of Lightning
Complete the Spell of Strength
Upgrade twice the Torch power-up
Complete the Spell for Invoking the Power of Wind
Upgrade any power-up for the first time
Destroy at least 100 imps
Complete the Spell to Imprison an Evil Spirit
Finish the first 10 levels with 3 stars in each level
Make a combo of 20x
Complete the Spell for Invoking the Power of Fire
Make a combo of 15x
Complete the Spell of Protection