Aside from the ads which I turn off, you cannot play the harder levels unless you bank a ridiculously high number of lower levels. Example: to play Hard level 43, you must reach level 780 (!) in boringly repetitive easy levels. This is really an excuse to force you to watch ads unless you turn off your wifi. There are also annoying interruptions about pointless, ugly "skins" and collecting rather silly puzzle pieces. They seem to do everything they can to actually prevent you from playing game.