Tandem Lookout

Oracle Text

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 Tandem Lookout is paired with another creature, each of those creatures has "Whenever this creature deals damage to an opponent, draw a card."

Card Rulings

3/14/2017 If Tandem Lookout or the creature it’s paired with is dealt lethal damage at the same time that either deals damage to an opponent, its ability triggers. You’ll draw a card even though that creature no longer has the ability.