Two Headed Giant - do I gain life when my teammate gains life?
No, the Pridemate's ability doesn't trigger when your teammate gains life, because while your shared life total goes up it is not you gaining life.

Two-Headed Giant FAQ:


  How does damage, loss of life, and gaining life work with the single life total for the team?
  Damage, loss of life, and gaining life happens to each player individually. The result is applied to the
  team’s shared life total.