Found it!
https://forum.atlas-games.com/t/collection-index-of-all-spell-mastery-abilities/2026/1
Mastery Ability Page Source
Acute Sense* 71 HoH:TL
Adaptive CastingΨ 99 HoH:TL
Boosted Casting†99 HoH:TL
Ceremonial CastingΨ 99 HoH:TL
Disguised CastingΨ 99 HoH:TL
Fast Casting 87 (83) ARM5:CR
Harnessed Casting†99-100 HoH:TL
Lab MasteryΨ 100 HoH:TL
Learn From MistakesΨ 100 HoH:TL
Magic Resistance 87 (101) ARM5:CR
Multiple Casting 87 ARM5:CR
Penetration 87 ARM5:CR
Quiet Casting 87 ARM5:CR
Stalwart CastingΨ 100 HoH:TL
Still Casting 87 ARM5:CR
Tethered Casting†100 HoH:TL
Imperturbable Casting 33 HOH:S
Obfuscated Casting 34 HOH:S
Precise Casting 34 HOH:S
Quick Casting 34 HOH:S
Unraveling 129 HOH:S
Rebuttal 129 HOH:S
Apotropaic Mastery 122 RoP:TI
- Quesitorial Magic (normally restricted)
Ψ Cult of Mercury (House Mercere)
†Mutante Magic (House Mercere)