Activate Duskmantle Guildmage's first ability by paying {1}{U}{B}, 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}{U}{B}, 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.
Repeat from step 2 for each other opponent.

Each opponent loses the game

Infinite mill

Near-infinite lifeloss

Duskmantle Guildmage

Mindcrank

Activate Duskmantle Guildmage's first ability by paying {1}{U}{B}.
Cast Maddening Cacophony with kicker by paying {4}{U}{U}, causing each opponent to mill half their library, rounded up.
Duskmantle Guildmage triggers for each card milled this way.
Resolve the first Duskmantle Guildmage trigger, causing the opponent to lose 1 life.
Repeat step 4 until the opponent loses the game due to having zero or less life.
Repeat from step 4 for each remaining trigger.

Combos with "Duskmantle Guildmage"