This is because it costs zero mana and immediately replaces itself in your hand once your opponent starts
Before its reprint, Ragavan, Nimble Pilferer would routinely sell for around $80, which was deserved as it was impressive
Fetch lands like Arid Mesa practically guarantee that you start with a land
Among main decks of Izzet Prowess builds specifically, 6 players are running four copies, 75 are running three copies, 32 are running two copies, 8 are running one copy, and 19 are running no copies of Vivi Ornitier
While I dont think Vivi is on the level of anything currently on the banlist, it does feel like a card that could be central to a future broken deck, especially if Mox Opal becomes part of the equation again
Outmuscle 3G Sorcery Put a +1/+1 counter on target creature you control, then it fights target creature you don't control