If you have "Robbin’ Goblin" on the field and attack with "Kycoo the Ghost Destroyer" or "The Bistro Butcher" both effects activate simultaneously. When attacking with "The Bistro Butcher" 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". When attacking with "Kycoo the Ghost Destroyer", since its effect is optional, the effect of "Robbin' Goblin" will Step 1 of the chain, and the effect of "Kycoo the Ghost Destroyer" will be Step 2.