When Spirit of Malevolence dies, each opponent loses 1 life and you gain 1 life.
If your life total is brought to 0 or less at the same time that Spirit of Malevolence is dealt lethal damage, you lose the game before its ability goes on the stack.
In a Two-Headed Giant game, Spirit of Malevolence's ability causes the opposing team to lose 2 life and you to gain 1 life.