Being able to pay for a spell without mana has a huge effect on play
Even if you're not reanimating something, getting rid of a key card in the graveyard is powerful enough on its own
Stormsplitter is a four-mana Otter Wizard
Looking back now, 5 mana is an awful lot to ask of an enchantment that doesnt do anything when it enters the battlefield, but if allowed to sit on the battlefield after a board wipe or a couple turns of play from an Aristocrats strategy (decks that derive value from sacrificing creatures), Black Market can quickly generate game-winning amounts of black mana
Mewtwo ex decks will slot in Mew ex for the same reason, to have more control in the mirror match, and this already appears to be having a positive effect on the Pokmon TCG Pocket meta by injecting some diversity
[61] Subsequently, cards are also available through e-commerce websites and individual sellers