1. Obli-Gator
  2. Obsolete Techie
  3. Obtuse Angler
  4. OctoBear
  5. Octopuss in Boots
  6. Offense Attorney
  7. Ogre Achiever
  8. Olfactory Worker
  9. Omnomnomnivore
  10. On-and-off Guard
  11. One-And-A-Halfling
  12. One-and-a-Halfling
  13. One-armed Archer
  14. One-Armed Archer
  15. One-armed Bandit
  16. One-Armed Bandit
  17. One-eyed Beholder
  18. One-Eyed Beholder
  19. One-hit Wanderer
  20. One-Hit Wonder
  21. One-legged Centipede
  22. One-Legged Centipede
  23. Onion Ringleader
  24. Onomatopoet
  25. Open Sorceror
  26. Operetta Phantom
  27. Optical Illusionist
  28. Optimus Slime
  29. Orc Angel
  30. Orc de Triomphe
  31. Orc of the Covenant
  32. Organ Grinder
  33. Origami Dragon
  34. Original Impostor
  35. ORLY Owl
  36. Orthodontisaur
  37. Oscillating Fanboy
  38. Ottoman Umpire
  39. Out-of-commissioner
  40. Out-of-Commissioner
  41. Out-of-Frame Monster
  42. Out-of-service Dog
  43. Out-of-Service Dog
  44. Out-of-shapeshifter
  45. Out-of-Shapeshifter
  46. Out-of-Tuna
  47. Out-Sorcerer
  48. Outsourced Monster
  49. Oval Lord
  50. Over-confident Noob
  51. Over-Confident Noob
  52. Overbearing Waiter
  53. Oxy-Moron
  54. Ozone Slayer