The following brief list of major changes in Monster Hunter 3 Ultimate(Wii U/3DS) when compared to Monster Hunter Tri(Wii):
General 1080p resolution support 3DS and Wii U games can connect to play together locally. G-Rank difficulty adds new challenges New companion Kayamba joins alongside Cha-cha. A companion can now join you in online mode when there is an empty slot. Awards system for completing certain tasks. (44 in total) Supports text chat with a gamepad (no longer requires USB keyboard, though that is an option alongside built-in voice chat) New Target Camera feature allows hunters to center the camera on nearby large monsters Touch screen can be used for item combining and map/menu All quests are available offline. Event quests now dowlonad instead of rotating. Once you download them, you can play them forever, whenever. Village now has low rank and high rank. Moga Woods Free Hunt now has Low Rank and High Rank (Day and night) Almost all Monsters now can appear except G Rank Monsters
Areas Sacred Land now has a ballista weapon for use Tower 3 area from Freedom Unite, an arena with rare monsters (Silver Rathalos, Gold Rathian, etc.) New Mountain Peaks area from Portable 3rd. Entire zone comparable in size to the other levels, with 9 sub-areas. A new town, Tanjia Port, replaces Loc-Lac City. A new 100% exclusive area, Disastrous Sea, is where players will fight Guran-Miraosu
Weapons/Armor 4 new weapon types join all weapons from Tri: Dual Sword, Gunlance, Hunting Horn and Bow. New element "blast" is added to the game. G-rank versions of old armor receive visual improvements New armor sets from all the new monsters New weapons from all the new monsters
Small Monsters Gargwa, a round bird. Zuwaroposu, a swamp herbivore. Bullfango, a wild boar. Anteka, an elk-like monster. Furogi, a relative to the jaggi with a poison element.
Large Monsters Plesioth, The Underwater Terror, Master of the Giant Lake Lagombi, a white rabbit beast "Dosufurogi", The Great Froggi Duramboros, the Hammer-Tail wyvern Nibelsnarf, Hunter Eater Nargacuga, the Living Shadow, Black Beast Arzuros, the blue bear beast. Volvidon, the volcanic armadillo Zinogre, the thunder wolf wyvern. Brachydios, the crushing wyvern