Rebound

The effect "When your opponent activates an effect that returns a card(s) on the field to the hand: Negate that effect, and if you do, choose 1 card from your opponent's hand or field and send it to the GY" is the effect processing performed when "Re-Bound" is activated. (This effect does not target.)

The activation of the card "Re-Bound" is an activation that chains directly to the activation of an opponent's monster effect that returns a card on the field to the hand, or the activation of an opponent's Spell/Trap card that returns a card on the field to the hand. (It cannot be activated in a chain to the activation of a Spell/Trap card's effect.)

When sending a card from your opponent's hand to the GY with the effect "choose 1 card from your opponent's hand or field and send it to the GY," you choose 1 card from your opponent's hand at random and send it to the GY.

The effect "If this Set card is destroyed by an opponent's card and sent to the GY: Draw 1 card" is an effect that activates in the GY and creates a Chain Link. (This effect does not target. It also activates during the Damage Step.)