What it does
Soulbond lets you pair two creatures when one enters the battlefield. When a creature with soulbond enters, you may pair it with another unpaired creature you control; conversely, when another creature enters, you may pair it with your unpaired soulbond creature. While paired, both creatures share the bonus granted by the soulbond keyword (printed on the soulbond creature).
The big nuance: pairing only happens at the moment a creature enters the battlefield—you can't pair already-existing creatures later. Each creature can only be paired with one other at a time, and both must be creatures you control. If either creature leaves or the pair is broken, both lose the bonus, and the surviving creature becomes unpaired (eligible to re-pair when a new creature enters).
In Commander, soulbond shines because creatures constantly enter from recursion, blinks, and tokens, giving repeated chances to re-pair and spread abilities like deathtouch, flying, or lifelink across your board.













