Starting with some of the most exciting aspects, there are a total of 73 different (both small and large) monsters, including all of the monsters from Monster Hunter Tri, most of the ones introduced in the Japan-only Monster Hunter Portable 3rd. On top of that, they added a couple of new subspecies and rare species and the brand new Brachydios!

New monsters from Monster Hunter Freedom Unite
  • Anteka (small)
  • Bullfango (small)
  • Azure Rathalos (subspecies)
  • Silver Rathalos
  • Pink Rathian (subspecies)
  • Gold Rathian
  • Plesioth
  • Green Plesioth (subspecies)
  • Black Diablos
  • Nargacuga


New monsters from Monster Hunter Portable 3rd
  • Gargwa (small)
  • Slagtoth (small)
  • Wroggi (small)
  • Arzuros
  • Great Wroggi
  • Lagombi
  • Volvidon
  • Nibelsnarf
  • Duramboros
  • Zinogre
  • Crimson Qurupeco (subspecies)
  • Purple Ludroth (subspecies)
  • Jade Barroth (subspecies)
  • Baleful Gigginox (subspecies)
  • Sand Barioth (subspecies)
  • Steel Uragaan (subspecies)
  • Glacial Agnaktor (subspecies)
  • Green Nargacuga (subspecies)


New to Monster Hunter 3 Ultimate
  • Brachydios
  • Rust Duramboros (subspecies)
  • Stygian Zinogre (subspecies)
  • Lucent Nargacuga (subspecies)
  • Ivory Lagiacrus (subspecies)
  • Abyssal Lagiacrus (subspecies)
  • Savage Deviljho (subspecies)
  • Hallowed Jhen Mohran (subspecies)
  • Goldbeard Ceadeus (subspecies)
  • ... and a brand new final boss!


Total number of weapons: 1,398 including the following
  • 59 Great Swords
  • 83 Long Swords
  • 71 Sword & Shields
  • 122 Dual Blades
  • 73 Hammers
  • 99 Hunting Horns
  • 78 Lances, 108 Gunlances
  • 76 Switch Axex
  • 91 Heavy Bowguns
  • 96 Light Bowguns
  • 115 Bows


Number of new quests: 211

Total number of quests: 339, not including DLC quest.

Number of new armour pieces: 1,028

Total number of armour pieces: 1,663

3 new areas: The Tower, Misty Peaks and the Tainted Sea

Total number of equipment: 3061

Monster Hunter 3 Ultimate will be released on March 19th in North America and March 22nd in Europe for the Nintendo 3DS and Wii U.

Source