Soulbond

The new soulbond mechanic lets creatures team up to fight side by side.



Wingcrafter U
Creature - Human Wizard (Common)
Soulbound (You may pair this creature with another unpaired creature when either enters the battlefield. They remain paired for as long as you control both of them)
As long as wingcrafter is paired with another creature, both creatures have flying.
1/1

When a creature with soulbond enters the battlefield, you may pair it with another unpaired creature you control. When another creature enters the battlefield under your control, if you control a creature with soulbond that isn't currently paired, you may pair it with the new creature.

The two creatures become unpaired if either of them leaves the battlefield, is no longer under your control, or stops being a creature.
Abilities—usually abilities on the creature with soulbond—will refer to paired creatures. There are no special rules about paired creatures beyond that. The two creatures still attack separately, block separately, get targeted by spells separately, etc.
A creature can only be paired with one creature at a time. (In other words, a pair of creatures is always two creatures.)

If you pair two creatures with soulbond, they'll both get both of the abilities they grant. For example, take a look at Silverblade Paladin:



Silverblade Paladin (1WW)
Creature - Human Knight (Rare)
Soulbound (You may pair this creature with another unpaired creature when either enters the battlefield. They remain paired for as long as you control both of them)
As long as Silverblade Paladin is paired with another creature, both creatures have double strike
2/2

If Silverblade Paladin and Wingcrafter are paired, they'll both have flying and double strike.

There are also a few cards in the set that don't have soulbond that refer to paired creatures.



Joint Assault G
Instant (Common)
Target creature gets +2/+2 until end of turn. If it's paired with a creature, that creature also gets +2/+2 until end of turn

As with any other targeted spell, Joint Assault will be countered if its target isn't legal when it resolves. (Joint Assault only has one target, even though it may affect multiple creatures.) So if you target a paired creature and it leaves the battlefield, gains protection from green, or otherwise becomes an illegal target, neither creature gets the bonus. If it's still a legal target but the creatures are no longer paired (say, because they're no longer controlled by the same player), only the targeted creature gets the bonus.