The creature database in Osmo Lettertopia shows you all the dream creatures you've collected. Dream creatures can be collected when you encounter them in each level.
Place the word that describes the creature to collect it. You'll collect the creature if you write a word that describes them and it crosses that character.
In the creature database, you can view all of the creatures you have collected so far and read information about them, such as what type of creature it is and the words that describe it.