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%) :
POE 3.19] How to Fit More Auras and Fix Your Mana Cost! Mana Reservation & Cost Guide - YouTube
Reservation - Path of Exile Wiki
Can Grace and Determination be 35% reservation just like Discipline? : r/pathofexile
Bug Reports - Helmet Corruption: 90% Mana Multiplier Not Working Correctly - Forum - Path of Exile
Reservation - Path of Exile Wiki
Reservation efficiency change is a slight meta shift, not a massive nerf. Do some math before you complain. : r/pathofexile
Bug Reports - Crimson Jewel Conqueror's Efficiency Reducing Max Mana - Forum - Path of Exile
How can I craft this helm? : r/pathofexile
POE 3.19] How to Fit More Auras and Fix Your Mana Cost! Mana Reservation & Cost Guide - YouTube
Bug Reports - Determination Mana Reservation Mastery and Blood Magic - Forum - Path of Exile
It Is Now Possible to Achieve 100% Reduced Mana Reserved : r/pathofexile
Feedback and Suggestions - Hide reserved HP/Mana for the mini hp bar also - Forum - Path of Exile
Development Manifesto - Aura Reservation and Reduced Mana Support Gem Change - Forum - Path of Exile
It Is Now Possible to Achieve 100% Reduced Mana Reserved : r/pathofexile