Champions need to lose some more mana and the bad finished mana items need to be improved.

The mage mana changes almost brought the class to a point where they were well-balanced but ultimately pidgeonholed builds and all but deleted a number of finished mana items from the game. Mages still have very little actual cost to their mana abilities once they finish a single LC item and the only thing keeping them balanced is the fact that most of them have rough AD lane matchups. Not to say the class is overpowered, but for the entire class's balance's sake this has to be addressed.

Many oppressive AD laners just don't care enough about mana. Jayce and Pantheon have been banes of top lane as they easily force a recall from many laners well before they go OOM. Give them some more relevance as the game goes on at the cost of their early mana rather than letting these cheeselords run rampant and create a toxic environment, win or lose.

Rod of Ages, Archangel's and GLP are all extremely weak. In a meta where games are decided rapidly, scaling-over-time finished items are utterly useless. In a MOBA with not only Flash but a plethora of hyper-mobile champions with all sorts of dashes, a non-instant slow with a cast time is irrelevant. Make these items relevant and powerful again to compensate for mages and AP tanks losing more mana.

Do marksmen even run out of mana? I don't know LOL

At any rate the first two issues sorely need to be addressed, or anyone new (the new mage included) or reworked that uses mana as a resource will forever be a taint on the game like Zoe.

Zoe.