Here is the full list of all 17 Halloween Mysteries achievements.
Complete the tutorial
Defeat the Pumpkin boss
Defeat the Toad boss
Defeat the Skeleton boss
Defeat the Daemon boss
Complete the whole game
Destroy the Ghost House
Loot everything in the tomb
Die within 5 sec
Kill 50 enemies
Collect 40 bugs
Kill the Nightshade lvl 10
Find all the bonus levels
Open 30 big chests
Kill a boss within 1 min
Complete a level within 7 min
Level up to lvl 50