To do that, either choose a permanent you control or reveal a card from your hand that fits the description
Mythic Rare Mythic rares are usually the splashiest cards in a set
Rogues and Pirates can make great use of this enchantment (they can go wide with small creatures), but Merfolk is probably the best fit
In 3% of Collector Boosters, you'll be able to find a Lost Legend : a card from 1994's set Legends that was found in an old Legends booster, opened up, and packed back into Dominaria United Collector Boosters
Ooze isn't totally outclassed by Klothys of course -- Ooze can exile things at instant speed (if you have the mana), Klothys cannot -- but I think overall I'd prefer the god for the GY hate slot in my decks
To finish setting up, each player takes six cards off the top of their deck and sets them to the side face down