The Battle Memory is a special item in Mother 3 in which the player can read about each individual enemy they have faced. The player can also 'test battle' the enemies and practice the music patterns in each battle. It is essentially the Mother equivalent of the Bestiary found in most RPGs. It can be found by Duster in Osohe Castle's library in Chapter 2.
In the original Japanese version of the game, battling against every single enemy in the game unlocks a silver star at the top of the Battle Memory. In The Unofficial Mother 3 Fan Translation, however, this has been changed slightly. Receiving the silver star also makes the final Frog in the game tell the player about a secret Memo menu that can be accessed by holding the L and R buttons while going into the Status section of the menu. However, this menu can be viewed without receiving the silver star and its information is added to as the game progresses. A gold star in the Battle Menu can be obtained by finding all the in-battle sprites of all enemies, front and back. This makes the final Frog tell the player that naming themselves 'HARD MODE' in the Forest Prayer Sanctuary will increase the difficulty level of all enemies, and that it can be changed back to regular difficulty when the player's name is requested again at the Clayman Factory. Again, this can also be done without receiving the gold star in the Battle Menu.