Betrothed

Replace {1} in one of your commanders' casting
costs with {w}. If none of your commanders have {1} in their casting costs, replace a coloured mana symbol instead.
Commander creatures you own have soulbond
and "As long as this creature is paired with
another creature, both creatures gain 'When a
paired creature leaves the battlefield, sacrifice this creature, gain 3 life, and draw a card.'"