Zynga has had a few articles in the news this year about possible copyright infringement. Games that closely resemble other games. Most notable is the fight Nimblebit had over Zynga's "Dream Heights" basically copy & pasting their Tiny Towers indie game. EA is also currently suing Zynga over claims that "The Ville" is a clone of Sims Social.
A few differences include "fusing" monsters to increase ability effectiveness and to breed new monsters. Players get monsters from Treasure Chests instead of the long grass. And in-game cash can be purchased with REAL cash. How Nintendo will take to this Zynga game, we'll have to wait and see.