More about Diamond Dude

If I use diamond dude's effect and the top card of my deck is Allure of Darkness, do I still need to remove a DARK monster from my hand? Because in the text it doesn't look like removing a Dark monster is a cost.

And what happens when I use his effect and Gold Sarcophagus is revealed?

1.- Banishing a DARK is part of Allure's effect. If you mill it with DD, you still have to banish a DARK OR discard your whole hand.

2.- "Select and remove from play 1 card in your Deck. During your second Standby Phase after this card's activation, add the removed card to your hand."
Gold Sarcophagus (the CARD) was never activated, only it's effect. You banish the monster, but you wont get it back.

woot