The Sandman: choose who carries the nightmare

Dream of the Endless leads a Dimir (blue/black) Commander deck built around Curses attached to opponents. At the beginning of your end step, Dream sends a Nightmare: an Aura Curse token attached to a target opponent that makes that player lose 1 life at the beginning of their upkeep. A player is haunted while a Curse you control is attached to them. The Sandman's realm becomes a battlefield strategy of placing those Curses and choosing how to exploit the resulting state.

• SEND A NIGHTMARE: Create a Nightmare Aura Curse token attached to a target opponent. At the beginning of the enchanted player's upkeep, that player loses 1 life.
• HAUNTED: A player is haunted while a Curse you control is attached to them. Dream of the Endless draws you a card whenever one of your creatures deals combat damage to a haunted player.
• THE ENDLESS RESPOND: Death of the Endless draws you a card and costs you 1 life whenever a creature controlled by a haunted player dies. Delirium of the Endless can send a Nightmare for two generic and one blue mana, once each turn.
• SPREAD THE DREAM: John Dee, Doctor Destiny sends a Nightmare to each opponent when he enters and stops haunted players gaining life. Rose Walker, the Vortex draws a card for each haunted opponent when she enters.

Spread the Curses or deepen the pressure

A single Curse is enough to establish the haunted condition, so reaching several opponents can open more useful attacks and improve Rose Walker's arrival. Dream rewards each creature that connects, rather than a single combined combat-damage event. Flying on the commander helps his own attacks, while other haunted payoffs let the rest of the deck benefit without requiring every card to send another Nightmare.

Lucifer Morningstar makes each haunted player sacrifice a creature on entry, and The Kindly Ones makes each haunted opponent lose life at your upkeep for every Curse attached to them. Those effects reward different distributions of enchantments. This The Sandman Magic Proxy deck suits players who enjoy persistent enchantment pressure, selective attacks and an interconnected cast whose effects read the same clearly defined condition.

A 100-card Commander deck plus 3 tokens, with the existing Bracket 4 designation.