Unfortunately, it lets the controller separate the piles, not the opponent, so the split often favors the Toymakers controller regardless of your decision
Its cheap and has a thing for noncreature spells, so I can see it in Jeskai combo decks that require using its abilities to generate card advantage
You don't need to control the permanent entering the battlefield, only the permanent that has the triggered ability
Previous Secret Lair precon decks, like last year's adorable puppies and kittens deck, and the angels deck with the stupid name, have sold out swiftly and currently fetch extravagant prices on the secondary market
Its smooth and efficient, and it fits into literally any dragon curve
The Earth King is at its best when you can curve a cheap 4-power creature into it, perhaps Surrak, Elusive Hunter in Standard