They pay the cost of either having to waste gold on useless stats, or not being able to buy certain items. Items like Archangel's Staff, Rod of Ages, Frozen Heart, and Iceborn Gauntlet are extremely powerful, but they're a lot of gold wasted for champions that don't benefit from the mana (and in the case of Archangel, it's entirely useless without mana).
And this brings a new balance philosophy to manaless champs. Either: (and note that when I say "mana" I include mana regen)
- Prohibit item purchases that have mana for manaless champs, like how Hunter's Machete is prohibited if not carrying Smite (not recommended).
- Add a "mana tax" to energy champs if they buy items that have mana (every mana item reduces your damage dealt by 2% and increases your damage taken by 2% if your champion does not utilize mana)
- Make mana more prevalent in the item store, appearing on more items, and keep the number of manaless items low.
I don't recommend 1) because of one particular champion -- Shyvana -- and the fact that Iceborn Gauntlet, even with its high cost and wasted stats, is still quite useful on her.
- would sadly only punish Bronze players for not knowing proper builds. It wouldn't nerf anyone because the item choices are available for manaless champions, even AP ones. But if we add 3) to that, it could be useful. Wanna build that QSS to counter Malzahar? Too bad, you're a manaless Zed, and you're gonna do reduced damage and take more damage if you build it because we decided to make it build from Null-Mantle and Sapphire Crystal. Wanna build that Zhonya's as a Katarina? Too bad, we added mana to it and now you're gonna hit less and take more. Do you like that Gunblade as Akali? Well good luck assassinating anyone with it, because you take more damage and deal less.
Maybe for clarity (because I know this would be an invisible value and frustrate new players), if a manaless champion tries to buy a mana item in the store, ask for a confirmation. "WARNING! This item has mana! As a champion that does not use mana, you will deal 2% less damage and take 2% more damage if you have this item. Do you wish to purchase this item?"