Keystone High Priestess

Each player plays with the top card of their
library revealed.
At the beginning of your upkeep, for each player
that has an Artifact spell on the top of their
library, create a 1/1 black Azra assassin token
creature with deathtouch.
Sacrifice an Azra creature: You may cast the top
card of target player's library if it is an artifact
until end of turn.