Hey you know how [kaya] have mana reduction but amplify spell dmg?

What if you have an item that [increase] mana cost but amplify spell dmg by 20%.

right now stacking mana, does 0 anything. it's actually stupid to stack mana and u actually have to build items that dont stack mana too much. HP always useful. Items like shiva is kinda wasteful in term of mana. Most hero cant use the extra mana.