Here is the full list of all 26 Don't open the doors! achievements.
Beat all the doors.
Read all the diary parts.
Find all the gold keys.
Break the beetlejuice cauldron.
Kill 1000 bugs.
Don't take any reward from Mr. Bee and pass through the hive gates.
Defeat the Arik.
Drink 200 pots of compote.
Explode the main door.
Upgrade diamond armor to max.
Squash 2000 objects.
Kill 50 spiders.
Defeat the Pumpkinello.
Kill 1000 flies.
Kill 50 bees.
Collect bee glue.
Die 25 times.
Squash 100 chests.
Carry a large amount of money.
Wear the glasses.
Defeat the Great Cactus.
Kill 10 enemies with a single hammer srike.
Kill 20 enemies with a single hammer srike.
Kill 5 enemies with a single hammer srike.
Find a book.
Bring the megabomb.