Snipe huner says ''... discard..., then...'', Arcfiend says ''... discard..., AND if you do....''. So Snipe's effect is only destroying a card the discarding is the cost of the effect. On the other hand Archfiend's effect is discard AND increase attack. So it's effect includes the discarding. And Dark Word monsters needs to be discarded by an effect, they don't work if they are discarded as costs
To plainly put it, Snipe Hunter discards not as an effect. Think of it as having too many cards in hand and discarding a card. Trance discards as a card effect. Card Effects and costs are two different things.
Anonymous
Lord Pancake
