Whenever another creature enters the battlefield, you gain 1 life.
10/4/2004 Does not trigger on a card on the battlefield being changed into a creature.
10/4/2004 The ability will not trigger on itself entering the battlefield, but it will trigger on any other creature that is put onto the battlefield at the same time.
8/1/2005 Two Soul Wardens entering the battlefield at the same time will each cause the other's ability to trigger.
8/1/2005 The life gain is mandatory.