You gain life equal to target creature's power. The next time that creature would deal damage this turn, prevent that damage.
You gain the life as soon as Dazzling Reflection resolves, not as the damage is prevented.
If two Dazzling Reflections targeting the same creature have resolved in the same turn, only one prevention effect will apply the next time it would deal damage. The other effect will apply if the creature would deal damage a second time later that turn.