Legends, religions, folklore, traditions and the like might provide good ideas for new creatures.
For example:
- Some Egyptian gods were half human, half animal. The scarab was their symbol of death and cats were considered holy by the ancient Egyptians.
- The Greek have dreamed up the centaur and Styx is the river of the dead, no mortal can cross (hhhmmmm... tile ideas, perhaps?)
- In Scandinavia the Troll is a supernatural being.
- Fairies have been dreamed up by the Celts. These are mischievous little creatures able to make things disappear.
- Whiches have been figured out by Christianity and Islam. These ladies have the mysterious ability to make things go wrong in their neighborhood.
- The Jews have invented the Golem. iirc it was intended as a beast of burden.
The point here being that there's a gigantic gold mine for creature ideas to be found in (ancient) culture. Things which are used to scare little kids into doing what you want and fairy tales are also a good source. No need to have the umpteenth wizard or knight when things could be made original simply by looking at what culture and history have to say.
We all wait for the witches characters and the apropriate rooms and items : culdruns , book receipts , cats , ravens , the separate system spell and learning path ...also don't forget to add the shakespearian intro when the first witch's hut is build in the game and player notice it : 
) 
