Capricious Phantasm

As Capricious Phantasm enters the battlefield, choose a number at random between 1 and 15. Capricious Phantasms power and toughness are equal to the chosen number.
At the beginning of your upkeep, choose a number at random between 1 and Capricious Phantasm's power, then Capricious Phantasm's base power and toughness become the chosen number.