Burn from Within deals X damage to any target. If a creature is dealt damage this way, it loses indestructible until end of turn. If that creature would die this turn, exile it instead.
4/8/2016 The damaged creature will be exiled if it would die for any reason that turn, not just if it dies due to damage from Burn from Within.
4/8/2016 If Burn from Within doesn’t deal damage to the target creature (perhaps because that damage was prevented or X is 0), neither additional effect will apply. It won’t lose indestructible, and it won’t be exiled instead of dying that turn.
4/8/2016 You can target a creature that doesn’t have indestructible with Burn from Within. It will still be exiled if it would die this turn.