Sunbond | Magic: The Gathering
Formats Sunbond is Legal in
Official Oracle Text for Sunbond
Enchanted creature has "Whenever you gain life, put that many +1/+1 counters on this creature."
Official Rulings for Sunbond
2/1/2014 : In a Two-Headed Giant game, life gained by your teammate won’t cause the ability to trigger, even though it causes your team’s life total to increase.