I already know the answer to this question, "Will Mad Reloader activate Dark World's effects?", which is no. But could someone explain why, and how I can tell whether or not a card's effect would activate the effect of Goldd, or the other Dark World monsters? Thanks in advance.

The reason why Mad Reloader does not work with Dark World is because Mad Reloader states that it "sends" cards to the Graveyard, not "discards" them. Dark World monsters must specifically be "discarded" in order for their effects to work.

As I just said, if a card specifically "discards" without the discard being a cost (usually costs are the first sentence ["Discard a card." or "Discard a card to activate this card"] or say something like "You can discard a card in order to..."), then it should work with Dark World monsters.

I was curious, does its effect work when the owner has no cards in hand?