Archivist of nightmares

Reach
Whenever Archivist of Nightmares enters the battlefield, you may draw a card and target player mills two cards.
Whenever a player mills a card, instead exile those cards with knowledge counters on them.
Once per turn and whenever Archivist of Nightmares dies, you may cast a spell or land with a knowledge counter from exile under your control.
Whenever Archivist of Nightmares dies, return all cards with knowledge counters on them from exhile into their owners graveyards.