Riverchurn Monument + Lord Xander, the Collector

Riverchurn Monument

Lord Xander, the Collector

How it works

1. Declare Lord Xander as an attacker, triggering its ability, causing an opponent to mill half their library, rounded down.
2. Activate Riverchurn Monument's exhaust ability by paying 2 and tapping it, causing each player to mill cards equal to the number of cards in their graveyard.