Each one provides a single Energy of the corresponding type pictured on the card, and you can play as many as you like in your deck
If you can't get enough of the Dark-type Eeveelution, then this will be one of the best values you find for any of its cards
With the lands in the cube he is typically quite powerful utility as well
And since we're going to be proliferating way more in general thanks to more Phyrexians dying with Brimaz, Blight of Oreskos, I'm adding more counters to the deck, such as Everflowing Chalice which is totally cracked when you're proliferating it, or oil counters like Vat of Rebirth and Norn's Wellspring, and even some poison cards like Ichor Rats which adds a secondary win condition if we come up against pillowfort or lifegain decks
While each one does it slightly differently, whether its mana cost, what they can target, or their base stats, theyre all similar enough that I think theyre equal in ability