well just beat monster rancher....kinda. i got to s rank then it starts to get boring. unlock some of the strong monsters with the help of the internet. i used the dragon to beat the s rank and after s rank theres ss and sss rank. thats kinda easy to get since the tournaments only got 4 monsters but the monsters do break the 999 limit. the game gets boring pretty fast and they did take off some monsters that im familiar with like the gabu or that raptor and the jelly dude.
this site basically helped me unlock the monsters:
http://www.monster-rancher.com/discus/index.html
