My son was playing in wizard city with 100 mana and after visiting friends locations, he now only has 57 mana, but full (meaning he can't go back to 100 mana no matter how many minigames he plays ). Is this a glitch?
Athames, Rings and other items can boost the maximum amount of mana that a player has but only while they are wearing the item.
For example, if your son traded in a hat that gave him a mana boost, for one that did not, his maximum mana will drop.
You can see the maximum mana that a character can have in their Character Screen, just press C on the keyboard when not in a duel. That page will show you all sorts of stats.