While it only does one thing, opening a game with a Dark Ritual into a commander like Yawgmoth, Thran Physician, or even Tinybones, Trinket Thief, and a Thoughtsieze on your first turn is pretty darn good
Not having to take a creature from the milled cards, and instead choosing anything in your yard
Outside of Kellogg being a remarkably cheap kidnapper, their actual card is only so-so
But they also carry Magic, and Pokemon, and Yu-Gi-Oh, because their small but dedicated customer base wants to buy those products and wants to buy them from a store that they want to support financially
How you designate the Energy in terms of the discard order determines what is discarded
It only reduces the cost of spells that another effect (such as that of Green Goblin's last ability) has allowed you to cast