I gotten 3/4 so far, but I don't know how to get the 4th one. I used the flamethrower class, riflemen class, cannon class so far but don't know the other name for the last class I need to get and how to get it. My explosives are lvl 50+ atm but so far I don't see the tome purchasable from the merchant. Does anyone know what I need to do to get it? Btw, I have the ! Special Battle now but don't know for sure if I should play it.