If there's a cost associated with having it attack, its controller isn't forced to pay that cost
Take Hollow One, which Mason Clark talked about in his most recent article
Tinker Time (Green-Blue-Red deck)100-card ready-to-play March of the Machine Commander Deck with 2 Traditional Foil Legendary cards and 98 nonfoil cards 10 Planechase cards and 1 planar die to trigger unique abilities and jump across the Multiverse 2-card Collector Booster Sample Packcontains 2 special treatment cards from the March of the Machine main set, including 1 Rare or Mythic Rare and at least 1 Traditional Foil card Deck introduces 10 never-before-seen MTG cards to Commander Accessories1 Foil-Etched Display Commander, 10 double-sided tokens, Life Tracker, and deck box The Best March of the Machine Commander Deck For Value Knights are the big winner in terms of financial investment
The reason Opt is so valuable is that it is instant, an effect easily worth a 25% decrease in power for this kind of card
A friend of mine used to run in my list the old green and black cycling land and switch them for the cycling duals, making room for the 3 others, and I totally supported his choice
The elves of Lorwyn are famous about feeling that others don't match up to their high ideal of perfection, so the ETB being a kill spell that kills non-Elves plays squarely into that flavor