Loremaster of the Arcane Arts (3.5e Feat)
From D&D Wiki
 Loremaster of the Arcane Arts [General]
[[3e Summary::You are a master of Critical Spell Success.]]
Prerequisite: ability to cast 2nd level arcane spells, Master of Spellcasting
Benefit: You cast a Critical Spell Success on the roll of a natural 19-20.
Normal: You cast a Critical Spell Success on the roll of a natural 20.
Special: This feat may only be used when using the Spellcasting variant.