Legend of the Guardians: The Owls of Ga'hoole

Well, this is the big grind trophy for this game. The trophy description is self-explanatory: you have to beat the game will all four owls. There is some good news, however, you do not have to complete any of the bonus missions. By your third or forth run, you'll know this game forwards and backwards and should be able to clear it in just over 2 hours.

One final important remark: I would recommend using up the extra save slots, as I don't know what will happen if you overwrite your old save files. There's no reason not to after all, as there are four save slots available.