Mana Stars are magic items used to increase maximum mana permanently. There are 3 types of mana stars, each type with a different mana bonus. One can only possess a maximum of 10 stars of each type, for a total of 65 maximum mana.
Note that the purchasable Mana Star in the Magic Shop must be bought first, to be able to get other Mana stars in the monster's loot bags. Thus, it's recommended to save the loot bags until the star is bought.
It's possible to get more than one per kind of monster, but they will all stop dropping stars once it reaches the maximum of 10.
Below is the drop rate of all mana stars from all areas. The ratio measures which area have better chances for a given type of star. The formula is:
$ DropRate*100/Cooldown $ where cooldown time is converted into one hour. The bigger the ratio, the better chance that area has.