This is for the monster you think Spiral knights should have [I am a player you will probably not see this monster in the
actual game].
I personally think there should be a Squidman like creature in the Beast family. He could be bipedal and have tentacles drop from his head. He would attack by whipping his tentacle at you or shooting clouds of ink laced with whatever status. He would probably have tentacles for arms.
One Squidman could possibly be calm and peaceful and tell about the Squidman and there history. Which would mainly be how the Squidmen were a once proud nation corrupted by a disease that alter the mind and made the Squidman act like a vicious beast. That Squidman would then tell you there are only a small amount of them left blockading their city to keep them safe.