These TCG rulings were issued by Upper Deck Entertainment and have since been deemed unofficial by Konami. They were previously considered official, but may or may not necessarily hold true nowadays.
If you don't have enough Life Points to pay for an Archfiend, the Archfiend is destroyed and you don't pay the cost.
You roll a die for Archfiends when your opponent resolves an effect that targets the Archfiend, not when it is activated. If the activation or effect of a card that targets your Archfiend is negated by some other card, then you do not roll a die for the Archfiend.