The Mana Reservation Efficiency mastery has been replaced as there is now a much larger amount of Mana Reservation Efficiency for Curse Auras on the passive tree." (The mastery was 30%) :
Development Manifesto - Aura Reservation and Reduced Mana Support Gem Change - Forum - Path of Exile
Mana - Path of Exile Wiki
POE 3.20 Best New Unique Items - Top 10 New & Reworked Uniques in Path of Exiles Forbidden Sanctum
New Unique Helmet [Heretic's Veil] : r/pathofexile
Aura | PoE Wiki
Scion - [3.12] Aura Stacker CI - 50ex Budget Guide | Upgrades to 500ex budget | Immortal - Forum - Path of Exile
POE 3.19] How to Fit More Auras and Fix Your Mana Cost! Mana Reservation & Cost Guide - YouTube
3.15] Spellslinger VD (Volatile Dead) & Detonate Dead Necromancer Gear, Jewels, and Flasks (PoE Expedition) - PoE Vault