Myr Battlesphere is a rare Artifact Creature — Myr Construct card from Scars of Mirrodin (SOM), collector number 180. Current market price: $0.34 (foil $14.29), TCGplayer market prices via Scryfall.
When this creature enters, create four 1/1 colorless Myr artifact creature tokens. Whenever this creature attacks, you may tap X untapped Myr you control. If you do, this creature gets +X/+0 until end of turn and deals X damage to the player or planeswalker it's attacking.