Magnus Yonweld, Patriarch

Insidious {5}{u}{b} ({5}{u}{b}: Exile this card from your hand. As long as it remains in exile, you may cast it without paying its mana cost.)
When Magnus Yonweld, Patriarch enters the battlefield, target player puts the top card of their library into their graveyard. If Magnus was cast from exile, that player puts the top twenty cards of their library into their graveyard instead.