Amethyst

Description
Restore 0.1 Mana when you cast a spell.

Strategy and Synergy
A good artifact for almost every deck. Gaining 0.1 when a spell is cast doesn't seem like a lot of  the player gains, but it stacks up pretty quickly. Especially in decks that focus on spamming out spells that have a Mana cost like -Decks, Amethyst can really boost the casting speed of the deck. can use the benefit to regenerate with  to cast spells with a higher Mana cost.

-Decks can't really benefit from Amethyst, since unlike, the Kunai are always at the end of the deck, making unimportant.

Trivia
Amethyst's flavor text references the origins of the Steven Universe character of the same name.