Some ideas for future dragon categories-names:
INSECTS: Ant, Fly, Wasp, Hornet, Spider, Beetle, Stinkbug, Cricket, Cockroach, Grasshopper, Ladybug.
WILD ANIMALS: Cheetah, Fox, Hyena, Lion, Kangaroo, Rhino, Hippo, Leopard, Wildebeest, Gazelle.
BIRDS: Vulture, Peacock, Ostrich, Canary, Toucan, Flamingo, Swan, Pelican, Albatross,
SEA ANIMALS: Crocodile, Frog, Sea Turtle, Seal, Walrus, Lobster, Oyster, Giant Squid, Crab, Shrimp,
FISH: Bass, Pufferfish, Piranha, Swordfish, Ray.
FOODS: Almonds, Peanuts, Walnuts, Raisins, Coffee, Milk, Tea, Taco, Pizza, Pie, Hotdog, Croissant, Paella.
FRUITS: Strawberry, Cranberry, Watermelon, Melon, Cherry, Apple, Avocado, Coconut, Fig, Lemon, Mango, Orange, Blackberry, Papaya, Pear, Peach, Pineapple, Apricot, Pomegranate, Blueberry, Guava, Raspberry, Lychee.
VEGETABLES: Broccoli, Leek, Spinach, Garlic, Tomato, Radish, Fennel, Turnip, Asparagus, Corn, Artichoke, Cucumber, Carrot, Onion, Cassava, Celery, Zucchini, Kale, Beet, Daikon, Radicchio, Parsnip, Kohlrabi.
FLOWERS: Lily, Lotus, Pansy, Jasmine, Sunflower, Rose, Tulip, Dahlia, Poppy.
ANCIENT GREECE GODS: Apollo, Ares, Hera, Hephaestus, Demeter, Aphrodite, Hermes, Dionysus.
ASTRONOMY: Comets, Nebula, Black Hole, Uranus, Venus, Mars, Saturn, Asteroid, Meteor, Neptune, Jupiter.
GEMS-MINERALS-METALS: Marble, Coal, Opal, Bronze, Silver, Agate, Garnet, Zircon, Sapphire, Onyx, Basalt, Malachite, Lapis Lazuli, Iron.
LANDMARKS: Sagrada Familia, Trevi Fountain, Eiffel Tower, Notre Dam, Louvre, Acropolis, Big Ben, Statue of Liberty, Leaning Tower of Pisa, Christ the Redeemer, Stonehenge, Golden Gate Bridge, St. Peter’s Basilica, Little Mermaid, Sydney Opera House, St. Basil's Cathedral, Versailles, Neuschwanstein Castle, Moai, Angkor Wat, Ponte Vecchio, Arc de Triomphe, London Eye, Burj Al Arab, Terracotta Warriors, Petronas, Hagia Sophia, The Forbidden, Atomium, Hollywood Sign, Tokyo Tower, Torii Gate, Brandenburg Gate, Westminster Abbey, Tower Bridge, Temple of Heaven, Burj Khalifa, Dancing House, Luxor, Santorini.
SPORTS: Basketball, Volleyball, Water Polo, Handball, Rugby, Archery, Boxing, Wrestling, Athletics, Canoe, Cycling, Wrestling, Gymnastics, Shooting, Swimming, Diving, Tennis, Taekwondo, Weightlifting, Golf, Billiard, Badminton, Table tennis, Darts, Skiing, Chess, Skating, Yoga, Sailing, Surfing, Rowing, Equestrian, Rafting, Bungee Jumping, Skydiving, Formula 1, Rally.
MUSIC INSTRUMENTS: Piano, Drum, Guitar, Violin, Saxophone, Accordion, Trumpet, Cello, Tambourine, Harp, Bongo.
FAMOUS PEOPLE: Steve Hawking, Mother Teresa, Nelson Mandela, Albert Einstein, Mahatma Gandhi , Elvis Presley, Vincent Van Gogh, Vladimir Lenin, Fidel Castro, Pablo Picasso, Sigmund Freud, Mao Zedong, Marie Antoinette, Marie Curie, Confucius, Socrates, Plato, Alexander the Great, Julius Caesar, Genghis Khan, Buddha, Marco Polo, Galileo Galilei, Napoleon Bonaparte, Nicole Tesla, Mary Magdalene, Sappho. Leonidas.
TECHNOLOGY: Computer, CD, Tablet, Phone, Camera, Video Camera, Keyboard, Typewriter, Printer, Radio, TV, MP3 Player.
JOBS: Acrobat, Policeman, Security Guard, Writer, Director, Chef, Pilot, Artist, Gardener, Architect, Archaeologist, Astronomer, Banker, Butler, Carpenter, Electrician, Farmer, Miner, Nurse, Plumber.
CHEMICAL ELEMENTS: Hydrogen, Oxygen, Helium, Carbon, Cobalt, Titanium, Zinc, Cadmium, Plutonium, Uranium, Lithium, Aluminium, Sulfur.
MUSIC STYLES: Pop, Rock, Punk, Country, Blues, Jazz, Hip Hop, Disco, R&B, Latin.
GREEK MYTHICAL CREATURES: Centaur, Charon, Charybdis, Erinyes, Griffin, Harpies, Minotaur, Scylla.
NATIONAL FOLK COSTUMES: Greek, American, Spanish, French, etc.

Chemical Elements sound cool, they could make an event with them (FYI I think there already is some of those dragons in game Hydrogen/Wildebeest etc)

As a fan of Greek mythology I like the creatures one as well.