Each time a monster you control inflicts Battle Damage to your opponent, your opponent discards 1 random card.
Rulings
Individual Card FAQs
If you have "Robbin' Goblin" on the field and attack with "Kycoo the Ghost Destroyer" or "The Bistro Butcher" both effects activate simultaneously. Since you control both effects you can choose the order that they go on a Chain, so you can have the opponent draw due to the effect of "The Bistro Butcher" and then discard for the effect of "Robbin' Goblin".
Trap|
Continuous