Arcane Crystal of Devastation, +2

Arcane Crystals are a further refinement of an Arcane Focus, serving to help the wielder amplify a particular aspect of the magical power they channel. Arcane Crystals do not require an attunement slot, but you can only equip a maximum of one Arcane Crystal equipped at any one time.

Whenever you cast a spell that makes a Spell Attack, you critically hit on a 18, 19, or 20.