A 5-mana black enchantment that turns every point of life you gain into a point of life loss for an opponent — and turns Exquisite Blood into an unwinnable-for-them loop.
The Sanguine Bond / Exquisite Blood loop. Any life gained triggers a drain, any life lost triggers a gain — together they spiral into an opponent's death with no further input needed.
Lifegain payoff decks. Even alone, it converts every lifegain trigger in an Orzhov or mono-black lifegain shell into reach and damage.
Aristocrats and drain decks. A deck already draining opponents with small effects gets each of those triggers doubled the moment any lifegain enters the mix.
How it does in Commander
As the commander
It's an enchantment, not a creature, so Sanguine Bond is never a commander — it lives entirely as a piece of the 99 in a deck led by something else.
In the 99
A strong include in any black lifegain or drain-focused deck, and a genuine two-card win condition the moment Exquisite Blood joins it — worth running as a value card even in decks not specifically hunting the combo.
Formats it's strong in
Lifegain and Aristocrats shells. The card is doing real work with the lifegain the deck already generates, combo or not.
Grindy, long Commander games. The longer a game runs, the more incidental lifegain triggers accumulate, and the more damage Sanguine Bond alone converts.
Formats it's weak in
Decks with little or no lifegain. With nothing triggering it, Sanguine Bond is a five-mana enchantment that does nothing.
Fast, low-interaction cEDH pods. Five mana for a card that needs a second piece to close the game is too slow next to a two-mana Thassa's Oracle line.
Synergistic cards
Exquisite Blood — The other half of the loop — together they turn any life swing into an opponent's death.
Vito, Thorn of the Dusk Rose — Doubles the life loss from any drain effect, which Sanguine Bond then converts into your own life total.
Blood Artist — A cheap, repeatable drain trigger that Sanguine Bond turns into steady incremental life swings all game.
Well of Lost Dreams — Another payoff that converts life gained into card draw, stacking with the damage Sanguine Bond is already dealing.
Is it worth the price?
Sanguine Bond itself is affordable; Exquisite Blood tends to cost a bit more as the piece most decks are specifically hunting for. Worth owning on its own merits in any lifegain shell, with the combo as a bonus rather than the reason to buy it.