Herald of Torment

The triggered ability that causes you to lose life applies whether Herald of Torment is a creature or an Aura. The "you" in that ability refers to Herald of Torment's controller. If you control Herald of Torment as an Aura enchanting a creature another player controls, that ability will trigger at the beginning of your upkeep and cause you to lose 1 life.

Unlike other Auras, an Aura with bestow isn't put into its owner's graveyard if it becomes unattached. Rather, the effect making it an Aura ends, it loses enchant creature, and it remains on the battlefield as an enchantment creature. It can attack (and its tap abilities can be activated, if it has any) on the turn it becomes unattached if it's been under your control continuously, even as an Aura, since your most recent turn began.

If a permanent with bestow enters the battlefield by any method other than being cast, it will be an enchantment creature. You can't choose to pay the bestow cost and have it become an Aura.