Duskmantle Guildmage and Mindcrank on the battlefield.
Each opponent has a life total that is less than or equal to their library size.
({1} magic symbol) ({U} magic symbol) ({B} magic symbol) plus an additional ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) for each opponent you have available.
Steps
Activate Duskmantle Guildmage's first ability by paying ({1} magic symbol) ({U} magic symbol) ({B} magic symbol) , causing your opponent to lose life whenever a card is put into their graveyard this turn.
Activate Duskmantle Guildmage's second ability by paying ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) , causing an opponent to mill two cards.
Duskmantle Guildmage triggers twice.
Resolve the first trigger, causing the opponent to lose 1 life.
Mindcrank triggers, causing the opponent to mill a card.
Duskmantle Guildmage triggers, causing the opponent to lose 1 life.
Repeat from step 5 until the opponent has a life total of zero, causing them to lose the game.