In Standard, it can be cast on Turn 2 after casting either Gilded Goose or Arboreal Grazer, and it plays particularly well with either one, in that Oko and Gilded Goose each make Food for the other one, so you can keep making mana or keep making Elks as needed, and with Arboreal Grazer, you can immediately turn the Grazer into an Elk and attack for three on Turn 2
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If this Pokemon has at least 1 extra Water Energy attached to it in addition to this attack's cost, when your opponent's Active Pokemon is Knocked Out by damage from those attacks, take 1 more Prize card
Dino fans of all kinds are well served by this deck
of 1993, called the Beta set, even has cards worth thousands of dollars