Arcane Specialist (5e Feat)
From D&D Wiki
Prerequisites: Ability to cast at least one spell
You can focus on single spell and cast it with greater efficacy. You gain the following benefits.
- Increase your spellcasting ability by 1, up to 20.
- After you complete a long rest, choose a spell from among the spells you know. Until your next long rest, you can cast this spell by expending a 1 level lower spell slot (minimum of 1st level spell slot) and you gain a bonus of +2 to spell attack roll / spell saving throw check for this spell.