If the player or creature that was targeted is no longer playing or on the battlefield when the damage would occur, the damage isn’t redirected.

The redirection protects both you and your creatures from the source. If the source would deal more than X damage to multiple objects, you decide which damage is redirected until X is used up. For example, your opponent casts a spell that deals 1 damage to you and 1 damage to two of your creatures. If you cast Shining Shoal with X = 2, you can have damage to you and one creature redirected to the target, or you could have damage to both creatures redirected.