Like the previous installments, this game involves the raising, breeding, and fighting of monsters. Monsters are created via a "Saucer Stone" regeneration system. Players must go to a Shrine, where they swap the Monster Rancher 4 disc with a CD, DVD, or another game disc. A monster is then generated from the data contained on that disc. Once a player regenerates a monster, they can raise it on a ranch, and train it to compete in battles. The limit for monsters depend on the size of their ranch but the maximum is 5 monsters. One of the features of Monster Rancher 4 is exploring different lands for rare items and to discover special monster breeds. The player's team of monsters accompanies them on these journeys, battling stray monsters and the "Boss" monster of each area. These battles can help raise the monsters' experience. At the beginning of the game, the player can only visit a limited number of areas, but as they progress through the game, they will be able to visit more advanced and dangerous areas. Some areas have special rare monster breeds that cannot be found anywhere else, and once the player finds these rare monsters, they will be able to regenerate them and raise them on their ranch. The four different lands you can eventually explore are the togle caves, the kalaragi jungle, the promiass ruins, and the volcano. Source: Wikipedia, "Monster Rancher 4", available under the CC-BY-SA License.