1 beast, fiend, ogre, giant, dragon, brute, demon, troll, bogeyman:
Why are so many children's fairy tales populated by monsters?
2 monstrosity, (living) abortion, mutant, mutation, freak, deformity, lusus naturae, eyesore, horror, miscreation, missing link:
Monsters of every description were the main features of circus sideshows for centuries.
2 monstrousness, heinousness, horribleness, horridness, hideousness, awfulness, nightmarishness, dreadfulness, frightfulness, horror, hellishness, ghoulishness, fiendishness, barbarity:
The monstrosity of the concentration camps was not widely known till after the war.