Xandyr, Identity Saboteur

Menace

When Xandyr enters the battlefield, each player
mills the top four cards of their library into their graveyard.
{2}{g/u}{g/u}: Each player chooses target creature card in their graveyard. Choose one of those cards at random, Xandyr becomes a copy of that creature except its name is Xandyr, it's legendary in addition to its other types, and it has this ability. Exile each other card.