Myr Battlesphere [Scars of Mirrodin]

Description

Set:	Scars of Mirrodin
Type:	Artifact Creature — Myr Construct
Rarity:	Rare
Cost:	{7}

When Myr Battlesphere enters the battlefield, create four 1/1 colorless Myr artifact creature tokens.
Whenever Myr Battlesphere attacks, you may tap X untapped Myr you control. If you do, Myr Battlesphere gets +X/+0 until end of turn and deals X damage to the player or planeswalker it's attacking.