Mana cost modifier
Returns the total amount of passive MP cost reduction available. This includes all modifiers such as Festival of Jarlsberg.
The CLI command "modtrace mana cost" provides a more detailed display.
Seefor further info on how MP reducers stack.
Most equipment and effects only allow up to -3 MP total, so the sum of your current effects may not match the actual amount of MP reduction (and therefore the value of this function).