+ 
+ 900g
250-1000 mana 30 armor 30 magic resist
Awe - Gain 1 armor and magic resist for every 50 mana. Refund 15% of mana spent
Upgraded active (reach full stacks) - Drain 100 mana per second to gain 30% damage reduction. Toggle with 15 second cooldown upon deactivation.
Anivia intensifies
I’d say make the passive offensive the same way seraph’s is defensive lol
Outrageous In Taric
Dat item can give you a total of +80 mr and ar with 1000 mana increase... And an active? Yeah idk about that.
Biggest issue: there's already a "defensive" tear option in the massive mana shield that 
gives you. This "defensive" option you have in mind is massively overtuned, and 
would just use this, his ult, and 
to be literally invincible, then kite your team all over the place...
would never die, 
would never die, 
, 
,
...none of them would die. 
would be a nightmare.
But by far the worst offender of this item would be Phase Rush 
. Same way as Singed: Build this item & Stoneplate, and be basically invincible while he stacks up his passive on an enemy. Since his W doesn't deal its damage until after he spits out his victim, Stoneplate wears off before he damages you, so you still take full damage from it. 60-70% dmg reduction off two active items + phaserush on Kench would mean he can invest the other 3 (he has to have swifties for that strat) into health/AP items instead of tank items, and still be too tanky to handle with less than 3 people hard focusing the hell out of him. And of course with phaserush, he's probably dragged you far away from anyone able to help you by then, and can easily finish you off.
Something like this, maybe?
It doesn't have to be a Frozen Heart rework, I just really like how the item name looks in this context.
Frozen Heart
Tear of the Goddess (850) + Aegis of the Legion (1100) + 650 = 2600
+30 Armor +30 Magic Resist +250 Mana
Unique - Awe: Grants bonus Armor and Magic Resist equal to 2% of your maximum Mana. Refunds 15% of Mana spent.
Unique - Mana Charge: Grants +4 maximum Mana whenever you expend Mana or take damage from an enemy champion or large monster (up to 3 times per 12 seconds).
Transforms into Heart of True Ice at +750 Mana.
/-/-/
Heart of True Ice
+30 Armor +30 Magic Resist +1000 Mana
Unique - Awe: Grants bonus Armor and Magic Resist equal to 2% of your maximum Mana. Refunds 15% of Mana spent.
Unique - Frostguard: Upon expending Mana, you gain Frostguard for 3 seconds, reducing damage from champion attacks and abilities by 20% of the Mana expended. Additional Mana expenditures will refresh Frostguard's duration, increasing it only if a greater amount of Mana is expended.
