u/rei2rei

Ok - Light of Deceit says: (Discard 2 cards.) Select up to 1 of your opponent's Cookies. That Cookie receives 2 damage. Then, you can [Equip] this card to your [Shadow Milk Cookie]. If there are 5 cards or less in your hand, during your turn, that Cookie receives -3 damage.

Which card is receiving the -3 damage? Shadow Milk? Or your opponent? Also, what is the benefit of attaching to Shadow Milk?

Help!