Last night as I lay thinking of monsters under my bed...

                                                              creeping
                                              crawling               crouching
                                 clawing                                         clamoring
                       crushing                                                             crunching
             cracking                                                                                 
        clutching
     clasping
   clipping
   cutting
   cleaving
        crowing
              craving
                      craven
                              cringing                                              cowering
                                                            crying

... there are a lot of monstrous words that begin with C.