It forces each opponent to sacrifice a non-land permanent when attacking, and gains 2 +1/+1 counters each time one of your artifacts enters the graveyard or exile from play
Its cosmic aesthetic and glowing foil finish give a sense of mystery and evolution
However a few do have "practical" uses - here are some examples: The particular card you reference, Garruk the Slayer, was created for the Magic 2015 prerelease and is used in a variant where one player plays normally and the other plays as Garruk
Gilgamesh offsets all of the downsides to playing equipment, and can create tons of value

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Havi, the All-Father You need a sacrifice outlet and Saffi Eriksdotter and you can start doing some cool loops with Havi, the All-Father