You can't download it without WiFi or Data plan. If you are playing online, you need data connection to connect with other players. Otherwise, there would be no one to play with you offline. Therefore, if you want to play serious, prepare an unlimited data plan for yourself before downloading it so that it won't affect your wallet much even though there would be nice benefits of using WIFI like no need to pay attention when playing the game, no need to fuss over the battery life and so on.