Athene's Unholy Grail
For the record I have read the change-list planned soon for mage items so this is based on that. Also I am making a separate post because there are so many comments now that any feedback is basically lost at this point if it has not already been read, this post can also be able to stand on its own since its a concept post.
First off I think Grail should remain as what it originally was created for which is a super mana regen item for mages and Archangels will be the super mana pool item for mages that also has the highest base ability power (balanced through the fact that you have to stack up your Tear).
The balance problem to Grail comes from the magic resist, not because it gives mana regen, since it is an item that gives a mage AP, CDR, mana regen, AND tankiness so makes someone like Ziggs and Xerath even safer with the added MR. If you removed the MR then when you catch these champions out they will die. Another thing is that I am pretty sure Riot wants mages to be more aggressive and less passive, since extreme passive play is the reason someone like Ziggs gotten nerfed a lot in the past, so there are better ways to make mana regen into a more aggressive stat without the need of making Grail into a trash item that no one can or will buy.
Also Mana Regen does encourage more action because it means a mage can keep fighting and scraping rather than running away when out of mana, and there are ways to fix the passive mana regen that DOES NOT involve remove mana regen items from mages.
Chalice of Harmony: Recipe: Amplifying Tome (435g) + Faerie Charm (125g) + Faerie Charm (125g) + 115g = 800g
Statistics: +25 Ability Power +50% base Mana Regen +UNIQUE Passive - Mana Font: Increase your total Mana Regen by 1.5% per 1% missing Mana.
Athene's Unholy Grail: Recipe: Chalice of Harmony (800g) + Fiendish Codex (800g) + 650g = 2250g
Statistics: +60 Ability Power +50% base Mana Regen +20% Cooldown Reduction +UNIQUE Passive - Mana Font: Increase your total Mana Regen by 1.5% per 1% missing Mana. +UNIQUE Passive - Mana Drain: Your basic attacks against champions deal 100(+25%AP) to 20(+5%AP) bonus magic damage based on your current Mana and grants 250% base Mana Regen for 5 seconds (5 seconds cooldown).
To clarify, current mana on a percentage so nothing is linked to how big your mana pool is, so if you have 100% mana then the damage is at its peak and 20% or less mana is when the damage is at its minimum. And so low damage means an insane burst of mana regen with my Grail passive and Mana Font working together; also Mana Font here I returned back to how it used to be where it increases your mana regen based on % missing mana rather than mana regen based on your missing mana and maximum mana pool.
Removing the magic resist makes Grail less of a ball of stats and greatly reduces the total cost because it no longer has the null magic mantle, plus making the item for aggressive mana regen rather than passive will greatly tone back infinite spell casting in siege scenarios on champions to far away to reach and properly fight back, so now to keep up their siege they must come into range of an enemy champion every so often to gain a massive boom to their mana regen, it also tones back champions like Ziggs' infinite waveclear forcing him to come within a much shorter basic attack range to get mana back. The cooldown is mainly for the damage proc and not for the insane base mana regen for a short time since this an effect over time already, but both are restricted by the cooldown anyways. But to restate it is against enemy champions ONLY to reward you for interacting with your opponent in a reasonable range you deal a little bit of bonus magic damage and a very large amount of mana regen for a short time, which again stacks with Mana Font (Mana Font applying after all your base mana regen values are added up).
Anyways, I believe this is all I wanted to say for now. So have a good day everyone and Riot PLEASE keep Grail as an item ANY mage can get supports already have a lot of high tier mana regen items including a Chalice items to themselves they do not need another one especially 2 Chalice items.