There are some sets where the cards are significantly better, flexible (used in more formats), or have a handful of rares that everyone is after
Thats still true of the Crystals, but more decks will want those for their secondary effects, and just consider the cost reduction a welcome bonus
Just slip him through your opponent's defenses a few times to rack up some Commander Damage, and you'll be the victor of the match in no time
In these previews, Wizards showcased Abaddon the Despoiler, the Commander of The Ruinous Powers deck
This is one of the most stable options for graveyard-centric play
Then you can also return two to the battlefield from your graveyard, and as you are churning through your deck discarding them, drawing two cards a pop, you'll easily have enough few to toss two onto the battlefield for free