Combat mana cost modifier
Returns the total amount of passive MP cost reduction available in combat. 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).