Breathkeeper Seraph

Flying, soulbond (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 Breathkeeper Seraph is paired with
another creature, each of those creatures has
"When this creature dies, you may return it to the
battlefield under its owner's control at the
beginning of your next upkeep."