"Which is Stronger!?" Series Set of 16 books There are no noticeable stains or tears, but the outer covers have been removed except for (Musk Ox vs. Elk). Musk Ox vs. Elk Owl vs. Porcupine Black Panther vs. Mandrill Mute Swan vs. Great Black-backed Gull African Wild Dog vs. Bush Pig Orangutan vs. Pangolin Pit Bull vs. Bobcat Giant Pacific Octopus vs. Sawfish Japanese Rhinoceros Beetle vs. Stag Beetle Masai Giraffe vs. Plains Zebra African Bullfrog vs. Giant Centipede Coconut Crab vs. Chicken Animals vs. Dinosaurs Komodo Dragon vs. Alligator Snapping Turtle Hippopotamus vs. African Buffalo Bighorn Sheep vs. Bison