I have been looking at the beast family of monsters and noticed that it is rather small. Only 5 types (including both snarby species). This means that there are only 3 non-boss beast monster groups.
Most are small or decent sized creatures.
Why not introduce a new kind of monster? Perhaps a crab species?
One that is slow and bulky and blows bubble bullets to stun knights so it can slam them with its claw?
http://www.mikedelaney.org/images/Img49.jpg