Item Concept: Grail of Tides
Cost: 
+ 
+600 gold (total of 2700g)
+60 magic resist +50% base mana regen
UNIQUE Active - Quicksilver: Removes all negative debuffs (90s cooldown) UNIQUE Passive - Harmony: Grants base hp regen equal to your base mana regen. UNIQUE Passive - Tidebreaker: When Quicksilver is used, gain 5% max hp and mana, 50% tenacity, and a 30% decaying movement speed bonus over 3s.
Trying to fix a few absent elements in the game. Mainly, a solid, general purpose MR item. Also, a QSS proc for mages and tanks that wont on its own be overpowered. Lastly, a solid use on its proc that will give tanks in particular a more significant boost when fighting mages in the heal-over-time from the Tidebreaker being stronger on them than on the mages or supports that would consider building this.
Plus, it builds out of chalice, which is a good bonus since nothing really builds out of it anymore.
or 
might suit the item better but this is a real good item - even if its stats/build path are super suboptimal or niche and doesnt end up being used all that often, it fills a need that existing itemization just doesn't.
40 AP is disgusting even with passive trying to help.