Battle Myrsphere (Playtest Card)

'When Battle Myrsphere enters the battlefield, reveal cards from the top of your library until you reveal a battle card. Put it onto the battlefield, and the rest on the bottom of your library in a random order.
Whenever Battle Myrsphere attacks, you may tap X untapped battles you control (so they're oriented like a regular Magic card). If you do, Battle Myrsphere gets +X/+0 until end of turn and deals X damage to the player or permanent.