In a Two-Headed Giant game, Invincible Hymn will essentially set your team’s life total to the number of cards in your library. For example, suppose your team has 8 life and you have thirty cards in your library. Your life total (being the same as your team’s life total) changes from 8 life to 30 life, for a net gain of 22 life. Your team’s life total becomes 30 (22 + 8).