Only the winners of the lottery were given the opportunity to purchase the gold Pikachu card for a whopping 216,000 (about $2,081)
The most likely reasons are if it's sacrificed, if it's legendary and another legendary permanent with the same name is controlled by the same player, if it's a planeswalker and another planeswalker with the same subtype is controlled by the same player, if it's a creature with toughness 0 or less, or if it's an Aura that's either unattached or attached to something illegal
And here comes the collecting: Gotta cathem all
In that case the card is not cast and simply remains where it is (which in the case of Omen Machine is the exile zone.) With a card like Wear // Tear, however, the situation is a bit more complex
Successful blink decks have existed in Modern before, thanks largely to Soulherder