[Kingly_Krab]

Here's some of the botspellsai.cpp code:

// manacost has special values, -1 is no mana cost, -2 is instant cast (no mana)
    int32 manaCost = mana_cost;

    if (manaCost == -1)
        manaCost = spells[AIspells[i].spellid].mana;
    else if (manaCost == -2)
        manaCost = 0;