Cast Cut Your Losses by paying {4}{U}{U}, targeting any player with an even library size.
Cut Your Losses' casualty ability triggers, allowing you to sacrifice a creature with power two or greater to create a copy of Cut Your Losses, targeting any other player with an even library size.
Resolve each Cut Your Losses, causing one or two players to mill their entire library.

Infinite mill for up to two target players

Cut Your Losses

Bruvac the Grandiloquent

Cast Cut Your Losses by paying {4}{U}{U}, causing the player enchanted by Fraying Sanity to mill half their library, rounded down.
At the beginning of your end step, Fraying Sanity triggers, causing the player to mill the rest of their library.

Combos with "Cut Your Losses"