Arcane Shield 2900 gold
60 ability power 50 armor 400 mana 10% cooldown reduction
Unique Passive : 15% of damage taken is dealt to your mana instead.
Unique Passive : 5% of damage dealt recovers your mana
Edit: I changed some of the numbers
I like the concept for sure. Would help out the more immobile mages in this AD meta
( 
)
I suggest a few tweaks. For one its way to cheap for what it does. if your going to balance it around price point do this:
70 Armor --> 50-40 Armor (70 armor is more than some tank items)
Unique Passive: 15% of damage dealt recovers that much mana (If you did this it would unbalance some champions and praticly give them unlimited mana. This would break 
im pretty sure. You could cast spells for free with this passive)
50 Ability power --> 60 Ability power (you'll see why)
100% Base Mana regeneration
2800 gold --> 3000 gold (That passive is just so strong)
These are just my opinions obvoisouly but i like the idea!
+ 
?
[{quoted}](name=Moonfall Saber,realm=NA,application-id=A8FQeEA8,discussion-id=9TIinXif,comment-id=,timestamp=2017-07-18T12:37:14.515+0000)Unique Passive : 15% of damage taken is dealt to your mana instead.
Slight adjustment should be either that you can toggle whether or not this is on or not or that it would be disabled when you're at 15% or less of maximum mana (or something among those lines, like 
). This is because some mages might as well be dead if they're at a certain mana threshold. 15% less damage taken is also pretty lackluster.
In terms of gold efficiency: 60 AP x 21.75 = 1305g 50 Armor x 20 = 1000g 400 Mana x 1.4 = 560g 10% CDR x 26.5 = 265g 1305 + 1000 + 560 + 265 = 3130g 3130/2900 = 107.93% Gold Efficiency
While not 
level, that's pretty up there.
An issue with this item, however, is that it's in direct competition with 
which has 10 more AP, 5 less armor, and can potentially block more damage and dodge CC while providing guaranteed 2.5 seconds of survival and the ability to zone. On top of that, providing 60 AP to mages and assassins compared to 70 AP is a huge gap for something that doesn't provide damage, only survivability. The only viability would be on tanks who benefit from this kind of AP such as 
,
,
... but even then you have to consider that it doesn't give that juicy HP that tanks enjoy. That means that these tanks will most likely buy them towards the end of their build (even after 
) just to abuse the fact that it's 15% multiplicative damage resistance. 
would be a "better" Arcane Shield in certain instances for that tank slot item and have a negative synergy between each other (its multiplicative, not additive).
Put this into perspective, 
provides significant amount of damage which justifies the 60 AP while 
grants 80 AP, 300 HP, 400 mana, and Eternity which could be ~40-100 extra HP. The extra 300 HP would generally be better than 15% less damage because 300 / .15 is 2000 -- you require 2000 damage to subtract 300 HP. This, however, doesn't factor in the damage resistances of 50 armor which means this 2000 HP number against physical damage is significantly less.
Now, another viable use of this item is that you can rush it in a match-up like 
or 
where surviving their all-in is all you need to win. However, you're still in competition with or even just because one shuts down the burst while the other is just super efficient for its cost. Arcane Shield is just kinda in the middle of mediocrity -- not very good lategame (in comparison to Zhonya's Hourglass) and not very great to rush early on (lack of damage) while not being very tanky either.
In other words, it's a very interesting item but it kinda gets overshadowed by other existing items in the game and lacks a solid identity in stats... only benefiting maybe AP Divers... but they would appreciate the active more. I could see and 
using this item because they have to be up close and personal and their kit (and RoA) have built-in sustain (Ryze's shield and Cass's E Heal) that synergies with damage resistances. However, it would be better with them if they gained a little more damage from it compared to (guess what) Zhonya's (pre-Seraph's) and Morellos (pre and post-Seraph's) (side note: 
can tank more damage and grants more AP at a cost that you have to stack it up... but the two can go together and Seraph's has to be charged up).
Scrap the passive for more AP.
Seems like a cool item to build out of .
Riot has specifically stated that they don't want there to be ways to "damage" mana. Maybe they'd allow this since it is on an item rather than a champion, but I feel like it would result in some very obnoxious gameplay (for both sides).
Interesting item, I like it. The passives are kinda cool, but I think it conflicts with what armor/ap items want to do. Also how it might interact with manaless champs could be wonky (even if they won't buy it anyways).
I think a more defensive based passive would be more suiting, maybe something like a ninja tabi passive or to go with the name you could have a passive similar to maw or steraks that would solidify it as anti-ad burst.
Also the cdr seems superflous especially when so many items already give it, maybe scrap it and make it a one or two hundres g cheaper?
So...it's like the Eternity passive, except based around damage, rather than spell casts?
Not bad but I bet this would break Ryze and Cassio (maybe Anivia too.)
The bottom passive might be a bit high. But I really like it.
